Geology of a part of the north end of the Gallatin Range, Gallatin County, Montana
by Russell Gene Tysdal
A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE IN APPLIED SCIENCE With a Major in Geology
Montana State University
© Copyright by Russell Gene Tysdal (1966)
Abstract:
In a 50-square mile area at the north end of the Gallatin Range, Gallatin County, Montana, about 4, 000
feet of sedimentary strata, ranging in age from Cambrian to Recent, is exposed. Rocks-of the Paleozoic
arid Mesozoic systems comprise a sedimentary sequence that does not exceed 3, 200 feet in thickness,
which is uncommonly thin when compared to equivalent sequences in neighboring areas.
The map area was apparently one of slower subsidence, and deposition of sediments proceeded less
continuously or at a slower rate. Ordovician, Silurian, Permian, Triassic, and Upper Cretaceous strata
are absent. Trilobites of the genus Glossopleura were found in the Cambrian Flathead Quartzite and are
the only known trilobites from the formation. Eocene volcanic rock overlies a major part of the
sequence, whereas Precambrian metamorphic rock underlies the entire sequence.
Analysis of the structural features of the map area and the adjoining region indicates that deformation
could have resulted from an east-northeast compressive stress applied during the Laramide orogeny.
The major northwest-trending fault in the map area is the South Cottonwood Creek fault, a reverse fault
with greater than 4,000 feet of throw. Sufficient evidence is presented to prove the existence of the
Gallatin Range front fault, a post-Laramide normal fault truncating the range on the north. ; GEOLOGY OF A.PART OF THE NORTH END OF THE GALLATIN
RANGE, .GALLATIN COUNTY,. MONTANA
by
RUSSELL GENE TYSDAL
A'thesis submitted to the Graduate Faculty in partial
fulfillment of the requirements for the degree
-of
MASTER OF SCIENCE IN APPLIED SCIENCE
With a Major in Geology
Approved:
Chairman, Examining'Committee
<5 ^ < ^ -3 ^ •
Graduate- Dean
.
MONTANA STATE UNIVERSITY
Bozeman, Montana
A ugust, 1966
iii
ACKNOW LEDGM ENTS
S in c e r e a p p r e c ia tio n i s e x te n d e d to th e N a tio n a l S c ie n c e F o u n d a tio n
f o r th e g r a n t w h ic h a id e d t h is stu d y and to th e D e p a r tm e n t of E a r th
S c i e n c e s , M on ta n a S ta te U n iv e r s it y , B o z e m a n , fo r m a k in g a v a ila b le
a p o r tio n o f th a t g r a n t to su p p o r t m y r e s e a r c h .
In p a r t ic u la r I w ou ld
lik e to th a n k D r . W illia m J. M cM a n n is fo r h is e d it o r ia l a id , f ie ld
g u id a n c e , and th e u n lim ite d u s e o f .h is p e r s o n a l lib r a r y ; ,
M o n ta g n e fo r h is a d v ic e on g la c ia l p r o b le m s ; and .
D r . John
D r; R o b e r t A.
C h a d w ic k fo r h is h e lp w ith ig n e o u s and m e t a m o r p h ic p r o b le m s .
T hanks
a r e a l s o d u e to M r. A l l i s o n R . P a lm e r f o r id e n t if ic a t io n o f in v e r t e b r a t e
f o s s i l s , to R o g e r W e g n e r fo r d o in g m u c h of th e d r a ftin g , a n d to N ita
P e r im a n fo r m a n u s c r ip t ty p in g .
A p p r e c ia t io n i s e x te n d e d to th e n u m e r o u s
la n d o w n e r s of th e m a p a r e a w ho g r a n te d u n lim ite d a c c e s s .
R . G. T.
T A B L E OF CO N TENTS
I N T R O D U C T I O N .......................
P r e v io u s I n v e s t ig a t io n s
L o c a tio n
T opography . . . . . .
C lim a te . . . . . . . .
L and E c o n o m ic s . . . <
A ccess
O b je c tiv e s .
o
*
«
e
*
*
o
a
o
e
o
S T R A T IG R A P H Y
P r e c a m b r ia n .
C a m b r ia n
O r d o v ic ia n
S ilu r ia n
D e v o n ia n
M is s i s sip p ia n
M i s s is s ip p ia n and P e n n s y lv a n ia n
P e r m ia n
. . . . . . . . . . . .
T r ia s s ic
J u r a s sic
C r e ta c e o u s . . . . . . . . . . . . . . . . .
I m p lic a t io n s of M a r in e S e d im e n t a r y S e q u e n c e
o
e
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
T e r tia r y
Q u a te r n a r y o o o o o o o o o o o o o o o e o o
0
0
0
0
0
0
0
0
0
0
0
9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
9
0
0
9
0
0
0
0
0
0
0
9
0
0
0
0
0
0
0
IG N E O U S R OCKS
0
0
o
0
0
o
0
0
.
O
0
9
O
0
O
O
O
0
0
0
0
0
0
0
0
0
0
IO
O
0
O
O
O
O
O
O
O
D
O
O
O
O
O
O
9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
9
9
0
0
0
0
0
9
0
0
0
0
0
0
0
0
0
9
0
0
0
0
0
O
Q
6
6
0
0
0
o
o
0
@
o
o
I
I
1
2
2
4
4
5
o
O
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
e
o
o
o
O
O
O
O
O
10
21
21
22
27
32
34
36
37
41
44
47
52
STRUCTURE
G eneral
. . . o . . . . . . . . . . . . . *
R e g io n a l T e c t o n ic P a t t e r n . . . . . . . . . . .
T e c t o n ic P a t t e r n s of A d ja c e n t A r e a s . . . . . .
S ou th C o tto n w o o d C r e e k F a u lt . . . . . . . . .
C r o s s F a u lt s . . . . . . . . . .
. . . . . . . .
L it t le B e a r C r e e k F a u lt and R e la t e d S t r u c t u r e s <
G a lla tin R a n g e F r o n t F a u lt
<
S u b s u r fa c e F a u lt s of B a s in
. . . . . . . . . .
57
57
58
60
65
72
76
79
GEO M ORPH OLOG Y. . . . . . . . . . . . . . . . . . . . . . . .
G la c ia l G e o lo g y . . . . . . . . . . . . . . . . . . . . . . .
E r o s io n S u r f a c e s . . . . . . . . . . . . . . . . . . . . . . .
83
83
86
C O N C L U SIO N S
88
.
R E F E R E N C E S C IT E D
. . . . . . . . . . . . . . . . .
82
. . . . . .
89
V
L IS T O F P L A T E S
P la t e I
G e o lo g ic m a p o f a p a r t o f th e n o r th end of th e
G a lla tin R a n g e , G a lla tin C o u n ty , M on tan a . . .
In p o c k e t
L IST OF F IG U R E S
F ig u r e I
In d ex M ap
F ig u r e 2
C r o s s - s e c t io n 's h o w ir ig p o s it io n of A lb e r t e lla
Z o n e - - G lo s s o p le u r a zo n e b o u n d a r y in th e
C a m b r ia n s t r a t a of w e s t e r n M o n ta n a ............................
F ig u r e 3
F ig u r e 4
F ig u r e 5
F ig u r e 6
F ig u r e 7
.......................................... ....
3
•
13
C h a r t c o m p a r in g t h i c k n e s s e s o f s e d im e n t a r y
u n its in th e m a p are,a w ith t h o s e in th e G a r n e t
M o u n ta in q u a d r a n g le . . • • • • > • • • • • • • • • •
46
M ap sh o w in g m a j o r s t r u c t u r a l f e a t u r e s of th e
r e g io n n-ear th e m a p a r e a
........................................................
59
E n la r g e d s p e c u la t iv e c r o s s - s e c t io n s , of
s tr u c tu r e 's a lo n g e a s t - t r e n d in g " e x t e n s io n o f
th e S o u th C o tto n w o o d C r e e k fa u lt ..........................................
-I
66
D ia g r a m m a t ic il lu s t r a t io n of d e v e lo p m e n t of
th e S o u th C o tto n w o o d C r e e k fa u lt at it s i n t e r ­
s e c t io n w ith th e W h e e le r G u lc h f a u l t .................................
70
S k e tc h of r e v e r s e d r a g r e l a t io n s h ip s a lo n g
tw o c r o s s f a u lt s .......................................... ............................. ....
76
•
/
vi
A BSTRA C T
In a 5 0 - s q u a r e m i l e a r e a at th e n o r th en d of th e G a lla tin R a n g e ,
G a lla tin C ou n ty , M o n ta n a , a b o u t 4 , 0 0 0 f e e t of s e d im e n t a r y s t r a t a ,
r a n g in g in a g e fr o m C a m b r ia n to R e c e n t , i s e x p b s e d . - R o c k s - o f the
P a l e o z o i c a r id * M eso z o ic s y s t e m s c o m p r is e a s e d im e n t a r y s e q u e n c e
th a t d o e s n o t e x c e e d 3, 2 0 0 f e e t in t h ic k n e s s , w h ic h i s u n c o m m o n ly
th in w h en c o m p a r e d to e q u iv a le n t s e q u e n c e s in n e ig h b o r in g a r e a s .
T h e m a p a r e a w a s a p p a r e n t ly one of s lo w e r s u b s id e n c e , an d d e p o s itio n of s e d im e n t s p r o c e e d e d l e s s c o n tin u o u s ly or at a s lo w e r r a te .
O r d o v ic ia n , S ilu r ia n , P e r m ia n , T r i a s s i c , and U p p er C r e t a c e o u s
s t r a t a a r e -a b sen t. T r i lo b it e s o f th e g e n u s G lo s s o p le u r a w e r e fou n d
in th e C a m b r ia n F la t h e a d Q u a r tz ite and a r e th e o n ly know n t r il o b it e s
fr o m th e fo r m a tio n . . E o c e n e v o lc a n ic r o c k o v e r l i e s a m a j o r p a r t of
th e s e q u e n c e , w h e r e a s P r e c a m b r ia n m e tarn or p h i c r o c k u n d e r lie s th e
e n t ir e s e q u e n c e .
_-__4
;
j
,
j:
-
j
iI
A n a ly s is of th e s t r u c t u r a l f e a t u r e s o f th e m a p a r e a and th e
a d jo in in g r e g io n in d ic a t e s th a t d e f o r m a t io n c o u ld h a v e r e s u lt e d fr o m
an e a s t - n o r t h e a s t c o m p r e s s i v e s t r e s s a p p lie d d u rin g th e L a r a m id e
o r o g e n y . T h e m a jo r n o r t h w e s t - t r e n d in g fa u lt in th e m a p a r e a i s th e
S ou th C o tto n w o o d C r e e k fa q lt, a r e v e r s e fa u lt w ith g r e a t e r th a n 4 ,0 0 0
f e e t of th r o w . S u f fic ie n t e y id e n c e i s p r e s e n t e d to p r o v e th e e x i s t e n c e
of th e G a lla tin R a n g e fr o n t fa u lt, a p o s t ^ L a r a m id e n o r m a l fa u lt
tr u n c a tin g th e r a n g e on th e n o r th .
;
I
!
;
i
j
!
*3 -
I’
4'
/
G EO LO G Y O F A P A R T OF T H E N O R T H E N D OF T H E G A L L A T IN
R A N G E , G A L L A T IN C O U N T Y , M O N T A N A
IN T R O D U C T IO N
P r e v i o u s I n v e s t ig a t io n s
T h e f i r s t g e o lo g ic m a p p in g in t h is an d c o n tig u o u s a r e a s w a s b y
P e a l e in 1889, th e r e s u l t s of w h ic h w e r e p u b lis h e d in 1 8 9 6 .
H is stu d y
o f th e T h r e e F o r k s o n e - d e g r e e q u a d r a n g le w a s of a r e c o n n a is s a n c e
n a tu r e .
H a c k e tt and o t h e r s (I 9 6 0 ) m a p p e d and b r ie f l y d e s c r ib e d th e
b a s in d e p o s it s of th e a d ja c e n t G a lla tin V a lle y .
M.- D . M ifflin (1 9 6 3 ,
U npub. M. S. T h e s i s , M on tan a S ta te U n iv . , B o z e m a n ) an d R o b in so n
(1 9 6 1 ) h a v e a l s o d e s c r ib e d s o m e o f th e s a m e b a s in d e p o s it s . . D a v is ,
K in o s h ita , and R o b in s o n (1 9 6 5 ) p u b lis h e d g r a v ity and a e r o m a g n e t ic
d a ta w h ic h c o n ta in s p e r t in e n t s t r u c t u r a l d a ta Sfor th e in c lu d e d p a r t of
th e G a lla tin V a lle y . . W. M . W eb er (1 9 6 5 , U n p u b .. M . S. T h e s i s , . M on tan a
S ta te U n iv . , B o z e m a n ) m a p p e d th e M id d le C r e e k a r e a j u s t e a s t o f th e
m a r g in of th e p r e s e n t w r i t e r ' s m a p a r e a .
U n p u b lish e d d a ta h a s b e e n
■made a v a ila b le b y W. J. M cM a n n is w h ic h h a s a id e d m a t e r i a l l y in th e
in t e r p r e t a t io n o f r e la t io n s h ip s , b o th w ith in th e m a p a r e a and in n e a r b y
'
areas.
L o c a tio n
T h e G a lla tin R a n g e , o f w h ic h th e m a p a r e a i s a p a r t, l i e s w ith in
th e s o u th e a s t e r n p a r t o f th e N o r th e r n R o c k y M o u n ta in p h y s io g r a p h ic
p r o v in c e o f F e n n e m a n (1 9 3 1 ). . T he m a p a r e a e n c o m p a s s e s a p p r o x im a t e ly
2
55 s q u a r e m i l e s in th e n o r th e r n p a r t o f th e G a lla tin R a n g e and f o o t ­
h i l l s at th e fr o n t o f th e r a n g e , th e B o z e m a n q u a d r a n g le b e tw e e n th e
I l l 0 O l' an d 1 1 1 ° 1 4 ' m e r id ia n s and th e 4 5 0 3 (j' and 4 5 ° 3 5 ' p a r a ll e ls .
T h e s m a ll to w n o f G a lla tin G a te w a y l i e s a p p r o x im a t e ly one m il e
n o r th of th e n o r t h w e s t e r n c o r n e r o f th e m a p a r e a , and th e to w n of
B o z e m a n i s a p p r o x im a t e ly s e v e n m i l e s n o r th o f th e n o r t h e a s t c o r n e r
1
o f th e m a p a r e a .
T opography
E le v a t io n of th e la n d r a n g e s fr o m 5, 0 0 0 f e e t at th e n o r th w e s t
m a r g in to g r e a t e r th a n 8, 600 f e e t a to p W h e e le r M o u n ta in in 'th e s o u th ­
if
e a st.
T h r e e - f o u r t h s of th e a r e a c o n s i s t s o f r u g g e d , h e a v ily f o r e s t e d
t e r r a i n w ith l o c a l r e l i e f c o m m o n ly v a r y in g b e tw e e n I, 5 0 0 f e e t and 2, 200
fe e t.
T h e b e s t r o c k e x p o s u r e s a r e g e n e r a l ly fou n d e l s e w h e r e th a n on
th e n o r t h e a s t s id e s of m o u n ta in s ; t h is s id e i s u s u a lly v e r y h e a v ily
f o r e s t e d w ith s m a ll (2 in c h d ia m e t e r ) e v e r g r e e n s an d b r u s h , ■and h a s
a th ic k s o i l m a n t le . • A t th e r a n g e fr o n t th e a r e a c o n s i s t s o f g e n t ly i n ­
c lin e d s u r f a c e s in t e r r u p t e d b y s t r e a m in c i s e d v a ll e y s .
C lim a te
;*
A s i s t y p ic a l of h ig h e r e le v a t io n s in th e R o c k y M o u n ta in s , d a ily
an d s e a s o n a l f lu c t u a t io n s of t e m p e r a t u r e r a n g e w id e ly .
M id d a y
t e m p e r a t u r e s d u rin g th e s u m m e r m o n th s a v e r a g e b e tw e e n 7 0 ° F and
8 0 ° F , w ith o c c a s io n a l e x t r e m e s in th e n in e t ie s .
W in ter d a y tim e
t e m p e r a t u r e s a r e g e n e r a l ly n e a r or b e lo w f r e e z in g , an d p e r io d s o f be,low
3
BOZEMAN
'LIVINGSTON
G A LLA TIN
'GATEW AY/
45°30'
F i g u r e I - In d ex M ap
'4
i
ij
4
Z el1O t e m p e r a t u r e s a r e c o m m o n in J a n u a r y and F e b r u a r y .
R are e x ­
t r e m e w in t e r t im e t e m p e r a t u r e s m a y g o a s lo w a s - 5 0 ° F .
S n ow
d e p th s in th e h ig h e r p o r t io n s of th e m a p a r e a m a y a v e r a g e a s m u ch a s
5 0 in c h e s d u r in g t h e - m id d le w in te r a n d e a r l y p a r t of s p r in g .
The
a v e r a g e a n n u a l p r e c ip it a t io n v a r i e s f r o m 20 in c h e s in th e lo w e r p a r t
o f th e m a p a r e a to a b o u t 30 in c h e s a t th e h ig h e r e l e v a t io n s .
G e o lo g ic
f ie l d w o r k i s f e a s ib le f r o m M ay th r o u g h O c to b e r a t lo w e r e le v a t io n s
au d June, th r o u g h S e p te m b e r at th e h ig h e r e le v a t io n s .
, T h e a b o v e c lim a t o lo g ic a l d a ta i s b a s e d on a n n u a l s u m m a r ie s
c o n ta in e d in th e U. S. W e a th e r B u r e a u 1s p u b lic a tio n , C lim a t o lo g ic a l
D a ta .
L a n d E c o n o m ie s
T h e m o u n ta in o u s r e g io n s of th e m a p - a r e a i s o w n ed p a r t ly b y th e
I:
■ N o r th e r n .P a c ific - R a ilr o a d and p a r t ly b y th e f e d e r a l g o v e r n m e n t.
The
r e g io n i s h e a v ily t im b e r e d , and th e m a in e n t e r p r i s e i s t r e e h a r v e s t in g
b y in d e p e n d e n t lo g g in g c o n c e r n s .
D u r in g th e s u m m e r and e a r l y f a ll,
h ig h op en a r e a s a r e u s e d a s g r a z in g la n d fo r b e e f c a t t le .
T h e lo w e r
r e a c h e s o f th e m a p a r e a - -th e f o o t h i l l s - - a r e p r iv a t e ly o w n ed and a r e
d o m in a n tly u s e d a s p a s t u r e .
T h e r e m a in d e r o f th e la n d i s ' u s e d fo r
d r y la n d a n d /o r ir r ig a t e d g r a in p r o d u c tio n , a lf a lf a or o th e r h a y c r o p s .
A ccess
N u m e r o u s r o a d s p e r m it y e a r a ro u n d a c c e s s b y c a r to th e f o o t h ills
a t th e fr o n t o f th e r a n g e .
T w o r o a d s p e n e t r a t e th e m o u n ta in o u s a r e a ;
i
5
on e le a d s up -M iddle C r e e k , th e o th e r up B ig- B e a r C r e e k .
N um erou s
lo g g i n g ■ro a d s" b r a n c h fr o m t h e s e tw o r o a d s , p e r m ittin g v e h ic u la r
a c c e s s to s o m e o f th e h ig h e r e le v a t io n s o f th e m a p a r e a .
A fo u r-
w h e e l d r iv e v e h ic le p r o v id e s th e b e s t c o n v e y a n c e on t h e s e r o a d s ,
a lth o u g h a . c o n v e n tio n a l p ic k u p -w ill s u f f ic e i f th e r o a d s a r e d r y .
B y fa r th e g r e a t e s t p a r t o f th e a r e a i s a c c e s s i b l e o n ly on fo o t or on
h orseb ack .
O b je c tiv e s
T h e o b j e c t iv e s of t h is stu d y w e r e to c o n s t r u c t a, g e o lo g ic m a p o f
th e b e d r o c k w ith in th e m o u n ta in o u s p a r t o f th e m a p a r e a , an d of the
s u r f i c i a l d e p o s it s a t th e fr o n t o f th e r a n g e ; to d e s c r ib e th e r o c k u n its
an d s t r u c t u r a l r e l a t io n s h ip s e n c o u n te r e d in c o m p ilin g th e g e o lo g ic
m ap ; and to d e s c r ib e th e g e o lo g ic d v e n ts th a t h a v e le a d to th e o b s e r v e d
r e la t io n s h i p s .
STRATIGRAPHY
P r e ca m b r ia n
M e ta m o r p h ic - R o c k s
P r e c a m b r ia n m e t a m o r p h ic r o c k s a r e e x t e n s iv e l y e x p o s e d in th e
s o u th w e s te r n and n o r t h e a s t e r n p a r t s of th e m a p a r e a , an d to a l e s s e r
e x te n t in th e s o u t h - c e n t r a l p a r t o f th e m a p a r e a .
G n e is s , a m p h ib o lite ,
s c h i s t , and m e t a q u a r t z it e - - in th a t o r d e r o f a b u n d a n c e - - m a k e up th e
m e t a m o r p h ic c o m p le x .
L a y e r in g i s w e l l d e v e lo p e d and g e n e r a lly
s t r i k e s N 4 5 -7 0 E and d ip s 5 0 - 7 5 S , w ith v a r ia t io n in d ip o c c u r r in g
e s p e c i a l l y w h e r e th e r o c k s a r e a s s o c i a t e d w ith fa u ltin g ; f o lia t io n is
p a r a ll e l to la y e r in g . - R e s is t a n t o u tc r o p s a r e g e n e r a lly s c a t t e r e d , w ith
d e e p ly w e a th e r e d s u r f a c e e x p o s u r e s o c c u r r in g in b e tw e e n .
L o c a lly ,
d e e p ly w e a th e r e d m e t a m o r p h ic r o c k s a r e d ir e c t ly o v e r la in b y th e
F la t h e a d Q u a r tz ite , s u g g e s t in g th a t p a r t o f th e w e a th e r in g o c c u r r e d
p r io r to d e p o s it io n of th e o v e r ly in g s e d im e n t a r y s e q u e n c e .
M o s t o f th e m e t a m o r p h ic r o c k s of th e m a p a r e a c o n s i s t of
a lte r n a tin g b a n d s o f m e d iu m - g r a y g n e i s s , p in k g n e is s , and a m p h i­
b o lit e .
T h e b a n d s c o m m o n ly g r a d e in to one a n o th er a n d r a n g e in t h ic k ­
n e s s fr o m a fe w f e e t to m o r e th a n 100 f e e t .
T h e m e d iu m - g r a y g n e is s is
th e m o s t c o m m o n o f th e t h r e e t y p e s a n d i s m e d iu m - g r a in e d ; c o m p o s it io n a lly it c o n s i s t s o f q u a r tz (4 0 -5 0 % ), m i c r o c l i n e (1 5 -3 0 % ), b io tite
(1 0 -1 5 % ), and m u s c o v it e (5-10% ).
T h e b io t it e i s d o m in a n tly b ro w n and
i s p r e s e n t b o th a s in d iv id u a l f la k e s and in m in u te b o o k s; m u c h o f th e
7
f e ld s p a r i s a lt e r e d to s e r i c i t e .
T h e -p in k g n e is s is m e d iu m - to c o a r s e ­
g r a in e d and c o n s i s t s o f q u a r tz (2 0 -3 5 % ), -m ic r o c lin e (2 5 -4 0 % ),
c l o s e (25-35% ),' and b io t it e (5 - 10%,).
o li g o -
M u ch o f th e o l i g o c l a s e i s u n ­
tw in e d ; it an d th e m i c r o c l i n e a r e e a s i l y m ist'a k e n fo r o r t h o c la s e
m e g a s c o p ic a lly j
T h e a m p h ib o lite i s d a r k ,. m e d iu m - to c o a r s e - g r a i n e d ,
g n e i s s i c , and r a r e l y s c h i s t o s e .
It c o n s i s t s of h o r n b le n d e , p la g io -
c l a s e , q u a r tz , b io t it e , and r a r e l y g a r n e t , in -th a t o r d e r of ab u n d an ce;
h o r n b le n d e i s b y far/-th e m o s t c o m m o n 1m in e r a l,- b u t th e p e r c e n t a g e s of
a l l c o n s titu te n t s v a r y s o g r e a t ly th a t a n a v e r a g e c o m p o s it io n w o u ld b e
■ m isle a d in g . . T h e h o r n b le n d e i s b la c k 'a n d c o m m o n ly o c c u r s a s stu b b y
p r is m s .
F e l d s p a r g r a in s a r e g e n e r a lly c l e a r , b u t s o m e a r e th o r o u g h ly
s a u s s u r it iz e d .
T h e q u a r tz i s c le a r and f o r m s o n ly a m in o r p e r c e n t a g e
of th e r o c k , a s d o e s th e b io t it e w h ic h ■o c cu r s a s g o ld -b ro w n , f la k e s .
G a r n e t a m p h ib o lite i s not. c o m m o n in th e m a p a r e a , and w h e r e p r e s e n t
th e g a r n e t s a r e p o o r ly d e v e lo p e d .
-At on e - lo c a lit y a n e a r l y 100% b la c k -
g r e e n h o r n b le n d e a m p h ib o lite m a y r e p r e s e n t an in t r u s iv e b o d y m e t a ­
m o r p h o s e d a f t e r e m p la c e m e n t .
M e ta m o r p h ic r o c k s e x p o s e d a lo n g th e -H y a lite C a n y o n r o a d d if f e r
•fr o m th e a b o v e -m e n tio n e d t y p e s in th a t th e y a r e a p p a r e n tly m o r e i n ­
t e n s e l y - d e f o r m e d - - p t y g m a t ic fo ld in g i s v e r y c o m m o n .
T h e p r e d o m in a n t
r o c k ty p e i s s im il a r to th e p r e v i o u s ly m e n t io n e d - m e d iu m - g r a y - g n e is s
e x c e p t th a t o l i g o c l a s e i s p r e s e n t an d g a r n e t s o c c u r lo c a lly ; s e r ic it iz a ,t io n
o f th e f e ld s p a r s i s l e s s c o m m o n .
T h e f o lia a r e g e n e r a l ly s t e e p ly
d ip p in g; s o m e f o li a d ip s t e e p ly to th e n o r t h w e s t a s o p p o se d to th e
d
(
c
(
{
I
8
g e n e r a l s o u th e a s t d ip o f th e m e t a m o r p h ic r o c k s in th e r e s t of th e m a p
area.
*
T h e d ip r e v e r s a l s m a y b e due to fa u ltin g , s o m e of w h ic h m a y
h a v e o c c u r r e d in P r e c a m b r ia n t im e .
It i s c o m m o n ly b e li e v e d th a t th e r o c k s w e r e o r ig in a lly a th ic k
■s e d im e n t a r y s e q u e n c e th a t w a s m e t a m o r p h o s e d and in tr u d e d b y ig n e o u s
m a g m a s , an d s u b s e q u e n t ly u n d e r w e n t a d d itio n a l p h a s e s o f m e t a m o r p h is m
( e . g . ,. s e e R e id ,
1957,
1963; M. • D . . M ifflin ,
M on t. S ta te U n iv . , B o z e m a n ).
19 6 3 , U npub. M . S. T h e s is ,
In th e T o b a cco - R o o t M o u n ta in s w e s t of
th e m a p a r e a , d e t a ile d stu d y of th e m e t a m o r p h ic c o m p le x b y R e id (1 9 6 3 )
in d ic a t e s th a t th e r o c k s h a v e u n d e r g o n e t h r e e m a jo r m e t a m o r p h ic
e p is o d e s an d tw o s t a g e s o f r e t r o g r a d e m e t a m o r p h is m .
T h e m e t a m o r p h ic
r o c k s p r e s e n t in the m a p a r e a and a d ja c e n t a r e a s su p p o r t R e id 's (1 9 6 3 )
in t e r p r e t a t io n of s e v e r a l p h a s e s of m e t a m o r p h is m , a s t h e y in c lu d e
m i n e r a l s and r o c k t y p e s c h a r a c t e r i s t i c o f lo w to h ig h g r a d e m e t a m o r ­
p h is m .
A n e x a m p le o f lo w g r a d e m e t a m o r p h ic r o c k o c c u r s im m e d ia t e ly
to th e so u th o f th e m a p a r e a in t h e ■NW 1 / 4 s e c .
14, T . 4S . , R . 4 E . ,
,(G arnet M o u n ta in q u a d r a n g le ) w h e r e an .a c t in o lit e s c h i s t i s p r e s e n t .
T h e g n e is s of th e m a p a r e a ( p r e v io u s ly d e s c r ib e d ) i s of m e d iu m to h ig h '
grade.
A p p r o x im a t e ly 6 m i l e s n o r t h w e s t o f th e m a p a r e a h ig h g r a d e
m e t a m o r p h ic r o c k s a r e r e p r e s e n t e d b y co y u n d u m b e a r in g s c h i s t s .
T h e m e t a m o r p h ic r o c k s of the m a p a r e a a r e p r e - B e l t in a g e and
a r e s i m i l a r to t h o s e t e r m e d P o n y m e t a m o r p h ic s in n e a r b y a r e a s (a s
o p p o se d to C h e r r y C r e e k m e t a m o r p h ic s ).
R e c e n t w o r k b y ,R e id (1957;
1963) in d ic a t e s th a t th e P o n y (y o u n g er), and C h e r r y C r e e k (o ld e r )
I
9
m e t a m o r p h ic s a r e p a r t of th e s a m e d e p o s it io n a l s e q u e n c e an d , t h e r e ­
f o r e , th e u n c o n fo r m ity th a t h a s b e e n s a id to l i e b e tw e e n th e tw o ( s e e
P e a le ,
1896; T a n s le y , S c h a f e r , and H a r t,
1933) a p p a r e n tly d o e s not
e x is t.
C o n s e q u e n tly , it i s th e r e c o m m e n d a t io n o f th e S t r a t ig r a p h ic
and N o m e n c la tu r e C o m m it t e e o f th e B illin g s G e o lo g ic a l S o c ie t y th a t
th e P r e C am b ria n m e t a m o r p h ic r o c k s b e t e r m e d " p r e - B e lt " and th u s
d is c o n tin u e u s e o f th e t e r m s P o n y and C h e r r y C r e e k , e x c e p t in th e
ty p e l o c a l i t i e s of t h o s e u n its (W. J. M c M a n n is, p e r s o n a l c o m m u n i­
c a tio n ,
1965).
G ile t t i (u n p u b lish e d m a n u s c r ip t ) h a s r e c e n t ly s u m m a r iz e d p r e l i m i ­
n a r y w o r k o f r a d io g e n ic a g e d a tin g in s o u th w e s t e r n M o n ta n a .
in d ic a te
H is d a ta
th a t a m a j o r p h a s e of r e g io n a l m e t a m o r p h is m o c c u r r e d ab ou t
1600 m . y.. a g o , and th a t th e s o u th e a s t m a r g in of t h is m e t a m o r p h is m is
lo c a te d a lo n g a n o r t h e a s t - s o u t h w e s t tr e n d in g " lin e" c r o s s in g the
G r a v e lly R a n g e and th e G a lla tin R iv e r C a n y o n .
th e r o c k s m a y b e 3200 m . y. old or o ld e r .
S o u th e a s t of t h is lin e
H e t e n t a t iv e ly s u g g e s t s th a t
s o m e of th e r o c k s in th e 1600 m . y. t e r r a n e a r e c o n s id e r a b ly o ld e r th an
1600 m . y. , b u t w e r e r e m e t a m o r p h o s e d 1600 m . y. a g o .
R a d io g e n ic a g e d e t e r m in a t io n s h a v e n o t b e e n m a d e on a n y o f th e
r o c k s o f th e m a p a r e a , b u t G ile t t i (u n p u b lish e d m a n u s c r ip t ) h a s d a ted
s o m e s a m p le s fr o m n e a r b y a r e a s . - A p p r o x im a t e ly 10 m i l e s n o r th w e s t
o f th e m a p a r e a , in th e A n c e n e y q u a d r a n g le ( s e c . 23, T . 2S. , R . 2 E . ),
a b io t it e s c h i s t w a s d ated a s 1550 m . y . o ld .
S ou th of th e m a p a r e a , in
th e G a r n e t M o u n ta in q u a d r a n g le , th e fo llo w in g d a te s w e r e ob tain ed :
iik
10
1690 m . y. (G r a n itic g n e is s ; s e c . 15, T-. 5S . , R . 4 -E . ), 1790 in . y.
( p s a m m it ic g n e is s ; s e c . 3 6 , T . 5 S. , R . 4 - E . ) , and 3 2 2 0 m . y . and
3270 m . y . . ( g r a n it ic g n e is s ; s e c .
o c c u r a p p r o x im a t e ly 7,
m ap area.
13, T . 6 S. ,. R . 4 -E . ).
The lo c a litie s
10, and 13 m i l e s , r e s p e c t i v e l y , so u th o f th e
T h e s o u th e a s t m a r g in of th e 1600 m . y. a g o m e t a m o r p h is m
a p p a r e n tly l i e s b e t w e e n 10 and 13 m i l e s so u th of th e m a p a r e a .
B e lt Supergroup
R o c k s of th e B e l t S u p e r g r o u p a r e n o t p r e s e n t in th e m a p a r e a ; th e
n e a r e s t o c c u r r e n c e df B e l t s t r a t a i s im m e d ia t e ly n o r th of an e a s t w e s t tr e n d in g lin e w h ic h t r a n s e c t s th e c e n t r a l p a r t o f th e B r id g e r - R a n g e
on th e, e a s t and th e H ig h la n d M o u n ta in s on th e w e s t .
T h e lin e i s b e ­
li e v e d t o b e a fa u lt zo n e th a t w a s a c t iv e in P r e c a m b r ia n B e lt t im e , p e r ­
m it t in g a t h ic k s e q u e n c e o f v e r y c o a r s e a r k o s ic B e l t s e d im e n t s to
a c c u m u la te on th e n o r th s id e (M c M a n n is ,
1 963).
C a m b r ia n
F la t h e a d Q u a r tz ite
T h e F la t h e a d Q u a r tz ite o f th e m a p a r e a i s f a ir l y c o n s is t e n t in' t h ic k ­
n e s s (4 0 - 7 5 fe e t ) an d u n c o n fo r m a b ly o v e r l i e s P r e c a m b r ia n m e t a m o r p h ic
r o c k w ith m a r k e d a n g u la r d is c o r d a n c e .
T h e f o r m a tio n c o n s i s t s of
m a rO o n , ta n , b r o w n , p in k , an d w h ite m e d iu m - to th ic k - b e d d e d and
m a s s i v e c r o s s - b e d d e d q u a r tz s a n d s to n e .
L o c a lly p r e s e n t i s a c r e a m
an d d u ll b r ic k r e d m o t t le d q u a r tz s a n d s t o n e , th e m o t t lin g b e in g
11 •
in d e p e n d e n t o f b e d d in g p la n e s .
T h e sa n d g r a in s V a r y in s i z e fr o m m e d iu m
to c o a r s e an d a r e s u b a n g u la r to a n g u la r .
L o c a l l y p r e s e n t sit th e F la t h e a d -
P r e c a m b r ia n - c o n ta c t i s (I ) a c o n g lo m e r a t e c o n s is t in g o f w e ll ro u n d ed
w h ite v it r e o u s q u a r tz c o b b le s in a m a t r ix o f c o a r s e - g r a i n e d q u a r tz s a n d ­
s t o n e , and (2) a r k o s ic m a t e r i a l th a t -rs•in p la c e s d if f ic u lt t o d iffe r e n tia te ,
f r o m th e u n d e r ly in g d e e p ly w e a t h e r e d P r e c a m b r ia n m e t a m o r p h ic -r o c k .
N e a r th e to p o f-th e fo r m a t io n th e s a n d s to n e c o m m o n ly c o n ta in s g la u c o n it e
and g r e e n i s h - g r a y m i c a c e o u s s h a le .
T h e F la t h e a d i s g r a d a t io n a l w ith
th e o v e r ly in g W o ls e y S h a le an d th e c o n ta c t i s t h e r e f o r e a r b it r a r y ; th e
a u th o r c h o s e th e b a s e of th e f i r s t p r o m in e n t s h a le zo n e a s th e c o n ta c t.
T h is b o u n d a r y i s in a g r e e m e n t w ith th a t o f D e i s s (T936) w ho e m e n d e d th e
d e fin itio n an d ty p e s e c t io n o f The f o r m a tio n .
T h e F la t h e a d i s g e n e r a lly
p o o r ly in d u r a te d , b u t s e e m s to b e b e t t e r in d u r a te d w h e r e th e fo r m a tio n i s
t h ic k e r ; th e t e r m s a n d s to n e i s m o r e a p p r o p r ia te th a n q u a r t z it e fo r th e
f o r m a tio n in th e m a p a r e a .
T h e F la t h e a d i s a b a s a l,, s lig h t ly t r a n s g r e s s i v e s a n d s to n e o f th e
C a m b r ia n s e q u e n c e , b e in g o ld er':in th e w e s t th a n in th e e a s t .
B e c a u s e of
th e a lm o s t t o t a l a b s e n c e o f f o s s i l s in th e -F l a t h e a d ,. th e a g e of' th e f o r m a t io n
■h a s b e e n in f e r r e d f r o m th e ( c o n fo r m a b le ) s u p e r j a c e n t W o l s e y S h a le . , T h is
p r o c e d u r e s u g g e s t s th a t th e F la t h e a d w a s d e p o s it e d d u r in g th e e a r ly M id d le
C a m b r ia n - - - A lb e r t e lla z o n e t im e - -(L o ch m a b ., B a lk ,
1 9 5 7 , p.
195 6, p. 616; L o c h m a n ,
13 2 ). . H o w e v e r , in a s u r f i c i a l d e p o s it in th e SW 1/4' SE 1 /4 s e c .
26,. T . 3 S ..,. R . 4 -E . , 'the w r it e r fo u n d t r i l o b i t e s ■of th e g e n u s G lo s s o p le u r a
r
w h ic h a r e d e f in it e ly fr o m th e F la t h e a d (th e f o s s i l s w e r e id e n t if ie d b y
/
12
A . R . P a l m e r , U . S. G e o lo g ic a l S u r v e y , W a sh in g to n , D . C. ), in d ic a tin g
th a t th e fo r m a t io n in th e m a p a r e a i s s lig h t ly y o u n g e r th a n p r e v io u s ly
b e lie v e d .
It i s d e f in it e ly y o u n g e r th a n th e F la th e a d in th e w e s t e r n p a r t,
o f th e s ta te w h e r e th e A lb e r t e l la fa u n a l e le m e n t s o c c u r in s h a le b e d s ,
w e ll up in th e o v e r ly in g W o ls e y e q u iv a le n t (S ilv e r. H ill F o r m a t io n ) , a n d th e G lo s s o p le u r a z o n e t h e r e i s in th e u p p e r p a r t o f th e s a m e fo r m a tio n
( s e e f ig . 2).
A p p r o x im a t e ly 35 m i l e s n o r t h w e s t of th e m a p a r e a th e
G l o s s o p le u r a fa u n a o c c u r s in th e lo w e r p a r t of th e W o ls e y (; A . . R . P a l m e r ,
1 9 6 5 , w r it t e n c o m m u n ic a tio n to W. J.' M c M a n n is).
W o ls e y S h a le
T h e W o ls e y S h a le r e s t s c o n fo r m a b ly on th e F la t h e a d Q u a r tz ite an d '•
i s c l e a r l y t r a n s it io n a l b e tw e e n th e la t t e r and th e o v e r ly in g M e a g h e r
L im e s t o n e .
T h e W o ls e y r a n g e s fr o m 40 f e e t t o 195 f e e t in t h ic k n e s s ,
in c r e a s i n g to w a r d th e so u th .
T h e 195 fo o t t h ic k n e s s i s h ig h w h e n c o m ­
p a r e d to th e c o m m o n r a n g e o f 40 f e e t to 80 f e e t in th e m a p a r e a and m a y .
r e p r e s e n t d e p o s it io n on a ir r e g u la r M id d le C a m b r ia n s e a flo o r ; th e .
W o ls e y i s t h ic k e r w h e r e th e F la t h e a d i s t h ic k e r .
C o m m o n ly , th e fo r m a -'
t io n i s p o o r ly e x p o s e d and f o r m s g r a s s c o v e r e d s lo p e s .
T h e b a s a l p a r t of th e W o ls e y c o n s i s t s o f g r a y - g r e e n s o ft f i s s i l e
v
m ic a c e o u s s h a le in t e r s t r a t if ie d w ith r e d d is h - b r o w n f in e - t o m e d iu m g r a in e d th in -b e d d e d a n d c r o s s - b e d d e d g la u c o n it ic q u a r tz s a n d s to n e .
L o c a l ly th e s a n d s to n e of th e b a s a l p a r t i s m e d iu m - and th ic k - b e d d e d ,
an d of th e ty p e fo u n d in th e F la th e a d .
T h e u p p er p a r t (3 /4 ) o f th e
fo r m a tio n c o n ta in s c h o c o la te b r o w n t o ' g r e e n f i s s i l e m ic a c e o u s s h a le ,
Philipsburg
Area
Logan
Area
Hasmark Dolomite
Silver Hill
Formation
Map
Area
Meagher Limestone
Glossopleura Zone
Wolsey Shale
Albertella Zone
Flathead
Quartzite
Flathead Quartzite
Precambrian Rocks
Figure 2. Cross-section showing position of Albertella zone— Glossopleura
zone boundary in the Cambrian strata of western Montana.
14
w ith s p a r in g ly in te r s t r a t if ie d b r o w n f in e - g r a i n e d q u a r tz s a n d s to n e .
W o rm t r a i l s an d c a s t s a r e c o m m o n on th e s h a le and s a n d s to n e .
In
th e u p p e r m o s t p a r t o f t h is u n it th e s a n d s to n e b e c o m e s m o r e co m m o n :
G r a y - g r e e n th in -b e d d e d and n o d u la r li m e s t o n e a ls o o c c u r s in th e
u p p e r m o s t p a r t, s o m e o f w h ic h c o n ta in s f o s s i l f r a g m e n t s .
A ccording-'
to L e b a u e r (1 9 6 4 ) m u c h o f th e g r e e n c o lo r o f th e W o ls e y i s d ue to th e
p r e s e n c e o f i l l i t e an d n o t c h lo r it e a s m a n y w o r k e r s h ad th o u g h t.
T h e a g e o f th e W o ls e y i s e a r l y M id d le C a m b r ia n , c o n ta in in g th e „
Z a c a n t h o id e s - G lo s s o p le u r a - K o o t e n ia z o n e s .
T h e f o r m a t io n i s t r a n s - ,
g r e s s i v e e a s tw a r d , w ith th e o ld e s t d e p o s it s b e in g in w e s t e r n m o s t
M o n ta n a (H a n so n ,
I 9 6 0 , p. 2 0 8 - 2 0 9 ) .
M e a g h e r L im e s t o n e
T h e M e a g h e r L im e s t o n e i s th e m o s t p r o m in e n t f o r m a tio n in th e ‘
m a p a r e a , e x h ib itin g a p e r s i s t e n t le d g e f o r m in g u n it b e t w e e n tw o n o n r e s i s t a n t s h a ly l i m e s t o n e u n it s .
T h e f o r m a t io n r a n g e s f r o m about 300 -
f e e t to 340 f e e t in t h ic k n e s s , and i s g r a d a t io n a l w ith th e s u b ja c e n t W o ls e y
S h a le an d th e s u p e r j a c e n t P a r k S h a le .
)
T h e lo w e r u n it ( 7 5 - 1 0 0 f e e t ) c o n s i s t s o f a b a s a l g r a y to y e llo w ru b b ly
l i m e s t o n e in te r b e d d e d w ith o liv e g r e e n f i s s i l e m ic a c e o u s s h a le ; lo c a lly
p r e s e n t i s a g la u c o n it ic li m e s t o n e p e b b le c o n g lo m e r a t e .
C o m p r is in g th e
r e m a in d e r of th e lo w e r u n it i s lig h t - g r a y to ta n tiiin and ir r e g u la r l y
b e d d e d d e n s e li m e s t o n e and in te r b e d d e d y e llo w - g r a y c a l c a r e o u s s h a le .
T h e lo w e r u n it is p o o r ly e x p o s e d and c o m m o n ly c o v e r e d .
15
T h e m id d le u n it (1 5 0 fe e t ) c o n s i s t s o f m e d iu m - g r a y to b r o w n th in
an d ir r e g u l a r l y b e d d e d d e n s e lim e s t o n e ( lo c a l ly f e t id ) , w ith th in i r ­
r e g u la r y e llo w o r o r a n g e s h a ly or s i l t y c a l c a r e o u s p a r t in g s th a t p r o d u c e
a c h a r a c t e r i s t i c g r a y o r b r o w n and o r a n g e m o t t lin g (H a n so n ,
1952, p. 14).
T h e y e llo w and o r a n g e c o lo r o f th e m o t t l e s i s due to th e p r e s e n c e of
lim o n it e (L e b a u e r ,
1965, p. 4 3 0 ).
A n a n a ly s is of th e lig h t ( y e llo w and
o r a n g e m o t t le s ) and d a r k c o lo r e d p o r t io n s f o r s a m p le s of th e M e a g h e r
f r o m th e L im e s to n e . H i lls (n o rth of th e m a p a r e a ) w a s r e p o r t e d b y
R u p p e l (1 9 5 0 , p.
18); th e a n a ly s is w a s m a d e b y H a r t z e ll (th en at th e
M o n tan a C o lle g e of M in e r a l S c ie n c e a n d T e c h n o lo g y , B u tte ).
s u lt s a r e a s f o llo w s :
S e g r e g a t e of l i g h t - c o l o r e d p o r tio n
I n s o lu b le (S: O2 ?)
14. 00
Ir o n and a lu m in a
3. 30
C aO (3 1 . 00) a s C a C O 3
55. 34
M gO (1 2 . 20) a s M gC O 3
25. 50
98. 14%
S e g r e g a t e of d a r k - c o lo r e d p o r tio n
S=Oz
4. 75
Ir o n and a lu m in a
2. 18
C aO (5 0 . 5) a s C a C O 3
90. 14
M gO ( 1 .2 5 ) a s M gC O 3
2. 60
99 . 67
%
T he r e ­
16
■L o c a lly -th e m id d le u n it i s m a s s i v e l y b ed d ed ' and c o n s i s t s o f b lu e
g r a y w e a th e r in g d e n s e li m e s t o n e .
,
V e r y - t h in d is c o n tin u o u s b ro w n 1
c h e r t s t r i n g e r s s p o r a d ic a lly o c c u r a t w h a t a r e o b v io u s ly f o r m e r b ed d in g
p la n e s .
T h e u n it f o r m s p r o m in e n t l e d g e s th r o u g h o u t th e m a p a r e a . '
T h e u p p e r 7 5 - 9 0 f e e t c o n s i s t s o f n o n - r e s i s t a n t y e llo w to g r a y t h in - .
b e d d e d and l o c a l l y n o d u la r f in e - g r a i n e d li m e s t o n e , w ith ab u nd an t y e llo w 1
s i l t y p a r t in g s .
T h e u n it i s v e r y p o o r ly e x p o s e d - in th e m a p a r e a and
o c c u r s a s a, g r a s s c o v e r e d s lo p e .
T h e - M e a g h e r 'L im e s t o n e i s o f m id d le -M id d le C a m b r ia n a g e - - c o n ­
ta in in g th e B a t h y u r is c u s - E lr a t h in a zo n e (L o c h m a n - B a lk ,
1956; pi. 6 1 7 ).
P a r L S h a le
T h e P a r k S h a le r a n g e s fr o m 40 f e e t to 70 f e e t t h ic k in th e -m a p a r e a , '
g e n e r a lly - t h ic k e n in g so u th w a r d . . T h e f o r m a t io n i s p o o r ly e x p o s e d and f o r m s g e n tly in c lin e d g r a s s y s lo p e s . . T h e P a r k c o n s i s t s o f g r e e n - g r a y
i
an d p u r p le -b r o w n f in e l y m ic a c e o u s f i s s i l e s h a le in te r b e d d e d w ith ta n
to b r o w n th in b e d s o f c a l c a r e o u s q u a r tz
s a n d s to n e .
L o c a lly , ■w o r m
c a s t s a r e p r e s e n t on th e s a n d s to n e . . T h e -fo r m a tio n c o n fo r m a b ly o v e r l i e s th e M e a g h e r and c o n fo r m a b ly u n d e r lie s t h e - P il g r im .
-It i s d i s ­
t in g u is h e d fr o m the W o ls e y S h a le b y th e s i z e o f th e m i c a f la k e s - - c o a r s e ­
g r a in e d in ,th e W o ls e y , f in e - g r a i n e d in th e P a r k .
T h e P a r k i s o f la t e M id d le C a m b r ia n a g e (L o c h m a n - Ba!Ik, 1956,
p. 617).
T h e P a r k - P i l g r i m c o n ta c t i s g e n e r a l ly c o n s id e r e d t o c o in c id e
w ith th e -M id d le C a m b r ia n - L a te C a m b r ia n t im e b o u n d a r y in t h is p a r t o f
M on tan a.
• 17
P i l g r i m L im e s t o n e
T h e P i l g r i m L im e s t o n e c o n fo r m a b ly o v e r l i e s th e P a r k ,Shale and
r a n g e s fr o m 245 f e e t t o 2 8 6 f e e t th ic k .
in to tw o m a jo r u n its:
T h e f o r m a tio n i s d i v i s i b l e
a lo w e r s lo p e - f o r m in g u n it th a t i s g e n e r a l ly -
p o o r ly e x p o s e d , and an u p p e r m a s s i v e le d g e - f o r m in g u n it.
T h e lo w e r u n it c o n s i s t s of l i g h t - g r a y to b u ff and p in k m e d iu m - to
th in k -b e d d e d l o c a l l y o o li t ic a n d /o r g la u c o n it ic f o s s i l f r a g m e n t a l l i m e ­
s to n e and li m e s t o n e p e b b le (fla t and e d g e w is e ) c o n g lo m e r a t e , w ith in t e r b e d d e d g r e e n c a lc a r e o u s s h a le .
T h e li m e s t o n e p e b b le s a r e o f th e fla t
ty p e , a r e w e l l ro u n d ed and fin e -? g r a in e d , w h e r e a s th e li m e s t o n e m a t r i x
i s m e d iu m - to c o a r s e - g r a i n e d and. l o c a l l y s a c c h a r o id a l.
T h is u n it i s
d o lo m it ic in th e u p p e r p a r t.
T h e u p p e r u n it i s d a r k b r o w n and t a n - g r a y m o t t le d t h ic k - and
m a s s i v e - b e d d e d le d g e fo r m in g m e d iu m - g r a in e d o o lit ic d o lo m it ic l i m e ­
s to n e .
T h e t a n - g r a y m o t t le s a r e r o u g h ly o r ie n te d p a r a l l e l to th e b ed d in g
■an d a r e d o lo m it ic w h e r e a s th e d a r k b r o w n a r e a s a r e li m e s t o n e o r s lig h t ly
d o m o m it ic li m e s t o n e .
M c M a n n is (1 9 5 5 , p.
1395) and B r o w n (1 9 5 9 , p. 260)
s ta te th a t th e m o t t lin g i s a p r o d u c t of p a r t ia l d o lo m it iz a t io n o f a p r e ­
e x i s t i n g o o li t ic li m e s t o n e ; M cM a n n is and C h a d w ick (1 9 6 4 ,, p. 8) n ote
e v id e n c e f o r a s e c o n d p h a s e of d o lo m it iz a t io n of th e u n it in p a r t s of th e
G a r n e t M o u n ta in q u a d r a n g le (a d jo in in g th e m a p a r e a to th e so u th ).
The
u p p e r fe w f e e t of th e u n it c o n ta in s a l i g h t - g r a y and y e l lo w m o t t le d th in -'
b e d d e d b r it t l e li m e s t o n e id e n t ic a l to th e M e a g h e r ty p e .
18
The- P i l g r i m i s o f la t e C a m b r ia n a g e ,(D r e sb a c h ia n ) and c o n ta in s th e
• C e d a r ia , C r e p ic e p h a lu s , and A p h e la s p is fa u n a l z o n e s ( L o c h m a n -B a lk ,
1 9 5 6 ,. p. 617).
- -R e d -L io n .F o r m a t io n
T h e R ed ' L io n F o r m a t io n c o n fo r m a b ly o v e r l i e s th e P i l g r i m L im e s t o n e
an d i s th e y o u n g e s t f o r m a t io n o f th e U p p er C a m b r ia n s e q u e n c e p r e s e n t in
th e m a p a r e a .
T h e R e d L io n i s a b ip a r t it e fo r m a tio n , c o n s is t in g of a
lo w e r s h a ly m e m b e r - - t h e D r y C r e e k S h a le - - an d an u p p e r u n n a m ed l i m e ­
s to n e m e m b e r .
T h e D r y C r e e k -S h a le M e m b e r is th e li t h i c an d a g e
- e q u iv a le n t o f the. D r y C r e e k -S h a le M e m b e r of th e S n ow y R a n g e -F o r m a tio n ;
th e li m e s t o n e m e m b e r i s th e a g e - -b u t n o t th e l i t h i c - - e q u i v a l e n t of th e
- S a g e P e b b le C o n g lo m e r a t e M e m b e r of th e S n o w y R a n g e .
T h e n a m e R ed
L io n i s u s e d h e r e b e c a u s e th e li m e s t o n e m e m b e r d e s c r ib e d h e r e in m o r e
c l o s e l y r e s e m b l e s th e lit h o lo g y of the. R e d L io n th an th a t o f th e Sn ow y
R ange.
The. D r y C r e e k t h ic k e n s fr o m 6 f e e t n e a r L a n g o h r N ob
I
to 20 f e e t
on W h e e le r M o u n ta in , w h e r e a s fo r th e s a m e tw o lo c a t io n s th e -lim e s to n e
m e m b e r i n c r e a s e s f r o m 70 f e e t to 95 f e e t , r e s p e c t i v e ly .
T h e D r y C reek",Shale M e m b e r i s a p o o r ly e x p o s e d u n it; i t c o n s is t s
o f o liv e g r e e n v e r y f in e ly m ic a c e o u s f i s s i l e - s h a le , in t e r s t r a t if ie d w ith
^ N am ed h e r e i n fo r th e p r o m in e n t to p o g r a p h ic h ig h in th e SE 1 /4 s e c .
36, T . 3 S. , R . 5 E .
19
o r a n g e and y e llo w s t a in e d b r o w n d e n s e s ilt s t o n e . - S o m e of th e s ilt s t o n e
i s s h a ly an d c o n ta in s ab u n d an t f in e g r a in e d m ic a f la k e s . . A th in l i m e -
•
^
• s to n e p e b b le c o n g lo m e r a t e b e d i s g e n e r a l ly p r e s e n t at th e b a s e o f th e
D r y C r e e k and s e v e r a l b e d s a l s o o c c u r a t th e to p of th e m e m b e r .
The -
l a t t e r c o n g lo m e r a t ic u n it i s 10 f e e t t h ic k w h e r e m e a s u r e d on W h e e le r <
V
M o u n ta in 1and i s of th e e d g e w is e or f la t - p e b b le ty p e .
T h e lim e s t o n e
p e b b le s a r e d e n s e su b r o u n d e d to ro u n d ed p e a g r e e n , ta n , w h ite , a n d ,
y e llo w and o c c u r in b e d s e x h ib itin g w a v y s u r f a c e s .
A t th e b a s e of th e u n n a m e d u p p e r li m e s t o n e m e m b e r i s a d a rk g r a y
w e a th e r in g m a s s i v e b io s t r o m a l c o lu m n a r lim e s t o n e , c o m p o s e d of th e
c a l c a r e o u s a lg a e C o lle n ia m a g n a F e n to n and F e n to n .
O v e r ly in g t h is •
b a s a l u n it i s 2 to 25 f e e t o f g r a y and ta n f in e to c o a r s e - g r a in e d t h in - ,
an d m e d iu m -b e d d e d li m e s t o n e and f o s s i l h a s h b e d s and li m e s t o n e p e b b le *
c o n g lo m e r a t e of th e ty p e th a t o c c u r s a t th e to p of th e D r y C r e e k .
Iy p r e s e n t i s in t e r c a la t e d o liv e g r e e n f i s s i l e s h a le .
S p a r in g -^
T h e r e m a in d e r o f th e
m e m b e r c o n s i s t s of m e d iu m - a n d t h ic k - b e d d e d and m a s s i v e g r e e n - b r o w n
li m e s t o n e w h ic h b e c o m e s th in -b e d d e d and d o lo m it ic in th e u p p er p a r t.
T h e lim e s t o n e b e d s a r e s e p a r a t e d b y y e llo w and o r a n g e s i l t y a n d /o r
c a l c a r e o u s s h a ly la m in a e th a t c o m m o n ly c o n ta in f o s s i l d e b r is .
In th e
m a s s i v e b e d s - t h e s e la m in a e o c c u r a s th in d o lo m it ic s t r in g e r s and
I
sta n d out on w e a t h e r e d s u r f a c e s .
C h e r t l e n s e s and s t r in g e r s a r e a lso -
c o m m o n in th e u p p e r p a r t of th e m a s s i v e b e d s and l o c a l l y ir r e g u la r
ch ert m a s s e s are p r e se n t.
T h e d o lo m it e o f t h is m e m b e r i s lig h t b r o w n
an d m e d iu m -g r a in e d o r s a c c h a r o id a l.
M c M a n n is and C h a d w ic k (1 9 ^ 4 , p. 8)
20
s ta te th a t th e s i l i c i f i c a t i o n an d d o lo m it iz a t io n of th e .R e d 'L io n , a s w e ll
a s th e s e c o n d p h a s e of d o lo m it iz a t io n o f t h e - P il g r im , a r e b e lie v e d to
b e th e r e s u l t o f a lt e r a t io n d u rin g e x p o s u r e - p r io r to 'D e v o n ia n d e p o s itio n .
. A c c o r d in g to D o r f and L o c h m a n (1 9 4 0 , p. 54 7 ) th e S n o w y -R a n g e
F o r m a t i o n - - t h e R e d L io n e q u iv a le n t - - a p p e a r s - t o b e th e e x a c t tim e
e q u iv a le n t o f th e F r a n c o n ia F o r m a t io n o f W is c o n s in .
L o c h m a n (1 9 5 0 ,
p. 2 2 1 3 ) s t a t e s th a t th e b a s a l c o lu m n a r li m e s t o n e of th e S n o w y R a n g e
'(Red L io n ) c o n ta in s t h e -E lv in ia zo n e o f th e s ta n d a r d C a m b r ia n s e c t io n .
G r o v e C r e e k .L im e s t o n e
In 1940 D o r f an d L o c b m a n f i r s t d e s c r ib e d th e G r o v e C r e e k l i m e ­
s to n e an d g a v e it f o r m a t io n a l s t a t u s .
L o c h m a n - B a lk (1 9 5 6 ) r e d u c e d th e
u n it to m e m b e r s t a t u s , c o n s id e r in g it th e y o u n g e s t m e m b e r o f th e S n o w y
R a n g e F o r m a t io n .
It a p p a r e n tly h a s no e q u iv a le n t in t h e R e d L io n . . T h e
G r o v e C r e e k L im e s t o n e i s n o t p r e s e n t in th e m a p a r e a b u t a th in to n g u e
o f it w a s m a p p e d b y R o b e r t s (1 9 6 4 ) in ,t h e - M y s t ic .L a k e q u a d r a n g le I 1 /2
, m i l e s to th e e a s t .
W. M. W eb er (1 9 6 5 , U n p u b lish e d M . S. T h e s i s , , M on t.
S ta te U n iv . , B o z e m a n ) c o u ld f in e n o t r a c e o f i t in th e in t e r v e n in g a r e a ,
b u t th e . o u tc r o p s in t h is a r e a a r e s o p o o r th a t n o d e f in it e c o n c lu s io n w a s
r e a c h e d c o n c e r n in g i t s d is t r ib u t io n .
T h e - t h ic k e s t k n ow n o u tc r o p of
G r o v e C r e e k i s o n ly 50 f e e t and a c c o r d in g t o L o c h m a n - B a lk (1 9 5 6 , p. 612)
r e m n a n ts o f th e f o r m a t io n a r e fo u n d o n ly " e a s t of a lin e ru n n in g fr o m th e
G a lla tin ; R a n g e s o u t h e a s t . . : to W in d -R iv e r C a n y o n in th e B r id g e r M o u n ta in s
o f W y o m in g . " T h a t im a g in a r y lin e a p p a r e n tly t r e n d s u p ,H y a lite C anyon;
21
th e G r o v e C r e e k w a s m o s t li k e l y r e m o v e d fr o m th e m a p a r e a b y p o s t C a m b r ia n , p r e - L a t e O r d o v ic ia n e r o s io n .
O r d o v ic ia n
B ig H o r n D o lo m it e
T h e B ig H o r n D o lo m it e (L a te O r d o v ic ia n ) i s n ot p r e s e n t in th e m a p
a r e a b u t w a s m a p p e d b y R o b e r t s (1 9 6 4 ) in th e M y s t ic L a k e q u a d r a n g le
2-| m i l e s to th e e a s t .
A c c o r d in g to h is m a p th e f o r m a tio n i s o n ly ab o u t
'
20 f e e t th ic k , no s t r a t a of w h ic h w e r e fo u n d b y W. M. W eb er (1 9 6 5 , U npub.
M . S. T h e s i s , M on t. S ta te U n iv . ,, B o z e m a n ) in th e in t e r v e n in g a r e a . - A
f e a t h e r e d g e o f th e f o r m a t io n h a s a l s o b e e n r e p o r te d in th e M a d iso n R a n g e
to th e s o u th w e s t ( S lo s s and M o r itz ,
1 9 5 1 ).
A t th e a b o v e tw o a r e a s w h e r e
th e f o r m a tio n c r o p s out, i t ' i s d e s c r ib e d a s " m a s s iv e d o lo m ite " .
T h ese
s a m e tw o a r e a s m a r k th e w e s t e r n m o s t a p p e a r a n c e o f th e f o r m a tio n a s
d e p ic te d on th e is o p a c h m a p s of S lo s s ( 1950) and R ic h a r d s an d
N e is c h m id t (1 9 5 7 ).
T h e p r e s e n c e o f th e f o r m a tio n in n e a r b y a r e a s , th e
la c k of e l a s t i c s th a t m ig h t s u g g e s t s h o r e lin e c o n d itio n s fo r r o c k s a t th e
p r e s e n t e d g e of th e f o r m a tio n , and th e e x t e n s iv e le n g th o f t im e th e f o r m a ­
tio n w a s e x p o s e d to e r o s io n (at l e a s t th e S ilu r ia n P e r io d ) , s u g g e s t th a t
th e B ig H o r n w a s r e m o v e d fr o m th e m a p a r e a b y e r o s io n .
S ilu r ia n
•S ilu r ia n s t r a t a h a v e n o t b e e n fou n d in w e s t e r n M o n ta n a ; th e r e g io n w a s
a p p a r e n tly a la n d s u r f a c e u n d e r g o in g e r o s io n . , In d eed , th e o n ly know n
22
S ilu r ia n s t r a t a in M o n ta n a o c c u r in th e n o r t h e a s t e r n p a r t o f th e s ta te in
th e s u b s u r f a c e o f th e W illis t o n B a s in .
S l o s s and M o r itz (1 9 5 1 ) n o te th a t
th e S ilu r ia n i s w e ll r e p r e s e n t e d in th e - L e m h i R a n g e , w e s t of th e Id a h o M on tan a b o r d e r , b u t t h e s e b e d s th in an d a r e tr u n c a te d s o u th w e s t of th e
border.
D e v o n ia n
- B e a r to q th .B u tt e and M a y w o o d F o r m a t io n s
N e it h e r th e B e a r t o o t h B u t t e - F o r m a t io n ( E a r ly D e v o n ia n ) n o r th e
M a y w o o d F o r m a t io n ( e a r l y L a t e 1D ev o n ia n ) w a s fou n d in th e m a p a r e a .
T h e B e a r to o th B u tte c o n s i s t s of " d isc o n tin u o u s e s t u a r in e and f lu v ia l
c h a n n e l- f ill d e p o s it s , s in k h o le f i l l i n g s , and r e g o lit h s " (S a n d b e r g ,
p.
1 3 0 1 ).
1961,
T h e f o r m a t io n o c c u r s a t s c a t t e r e d l o c a l i t i e s in ,the B e a r to o th
■R a n g e an d p o s s i b l y a t l o c a l i t i e s f a r t h e r n o r t h w e s t , b u t i s a p p a r e n tly
a b s e n t fr o m t h e ■G a lla tin R a n g e (M c M a n n is,
1962).
It i s p o s s i b l e th a t th e
B e a r to o th ,B u tte w a s d e p o s it e d in th e m a p a r e a and s u b s e q u e n t ly r e m o v e d
b y e r o s io n ; h o w e v e r , c o n s id e r in g th e c h a n n e l- f ill n a tu r e o f th e fo r m a tio n
an d i t s a p p a r e n t a b s e n c e f r o m th e e n t ir e G a lla tin R a n g e , it i s m o r e li k e l y
th a t th e fo r m a t io n w a s n e v e r d e p o s it e d in th e m a p a r e a .
T h e M ay w o o d
c o n s i s t s of l i m e s t o n e , d o lo m it e , and m u d s t o n e , .and c o n fo r m a b ly u n d e r lie s
th e J e f f e r s o n - L im e s t o n e .
T h e n e a r e s t o u tc r o p of th e f o r m a t io n is 2-| m i l e s
so u th of th e s o u th w e s t c o r n e r o f th e m a p a r e a ,, w h e r e it w a s I'd e p o s ite d in
m a r g in a l - m a r in e b r a c k is h o r f r e s h w a t e r s , w h e r e a s at m o s t know n
23
lo c a t io n s d e p o s it io n w a s in s h a llo w , o p en , or s lig h t ly r e s t r i c t e d m a r in e
w a te r s"
(S a n d b er g and M c M a n n is,
1 9 6 4 , p. C 5 0 ). , T h e m a p a r e a w a s
a p p a r e n tly n e a r a s h o r e lin e w h en the' M a y w o o d w a s d e p o s it e d a t th e a b o v e
lo c a tio n , and th e a b s e n c e of th e fo r m a t io n s u g g e s t s th a t th e m a p a r e a
V
w a s s t i l l a b o v e s e a l e v e l a t th a t t im e .
■J e ffe r s o n - L im e s t o n e
T h e J e f f e r so n - L im e s t o n e d i s c o n fo r m a b ly o v e r l i e s th e R e d L io n w ith
a n ir r e g u la r c o n ta c t. 1 T h e f o r m a t io n i s 2 5 4 f e e t t h ic k a lo n g B ig B e a r
C r e e k , th in n in g s lig h t ly e a s t w a r d to th e L a n g o h r N ob a r e a w h e r e it is
a p p r o x im a te ly 225 f e e t t h ic k . - S tr a ta o f th e f o r m a tio n a r e d iv is ib le
in to tw o u n its :
(I) a lo w e r s lo p e - f o r m in g u n it, c o r r e la t e d w ith,the"
D u p e r o w F o r m a tio n ,'o f'th e W i l l i s t on. B a s in b y S a n d b e r g a n d 'H a m m o n d
(1 9 5 8 ) an d d e s ig n a t e d th e " lo w e r m e m b e r " b y S a n d b er g (1 9 6 5 , p.. N S),
an d (2) an u p p e r le d g e - f o r m in g u n it, c o r r e la t e d w ith th e B ir d b e a r
F o r m a t io n of th e W illis t o n B a s in b y S a n d b e r g and H a m m o n d (1 9 5 8 ) and
d e s ig n a t e d th e " B ir d b e a r M e m b e r " b y S a n d b e r g (1 9 6 5 , p. N 7 ).
T h e lo w e r m e m b e r c o n s i s t s o f d a r k b r o w n ,to d a r k g r a y w e a th e r in g
m e d iu m b r o w n to ta n m e d iu m - b e d d e d to 'm a s s iv e f i n e - to -m e d iu m - g r a in e d
s a c c h a r o id a l d o lo m ite and d o lo m it ic l i m e s t o n e .
In th e u p p e r p a r t o f th e
lo w e r m e m b e r - t h e s e s t r a t a a r e c o m m o n ly c o a r s e - g r a i n e d , lo c a lly c o n ta in
q u a r tz s a n d ,. and a r e o n ly m o d e r a t e ly in d u r a te d .
I n t e r s t r a t if ie d a r e th in
b e d s of lig h t b r o w n to p in k and y e llo w d e n s e and c o m m o n ly s h a ly d o lo m ite
and d o lo m it ic lim e s t o n e ; t h e s e b e d s a r e m o s t p r e v a le n t in the:-upper o n e h a lf of th e lo w e r m e m b e r .
S o lu tio n b r e c c i a z o n e s a r e c o m m o n in th e
24
u p p e r p a r t o f th e lo w e r m e m b e r , and o r a n g e w e a th e r in g b r o w n and g r a y
c h e r t l e n s e s , n o d u le s , an d s t r in g e r s a r e p r e s e n t a t v a r io u s h o r iz o n s in
th e m e m b e r .
M o s t of th e b e d s h a v e a s tr o n g p e t r o lif e r o u s o d o r on
fr e s h fr a c tu r e .
T h e B ir d b e a r M e m b e r i s a p p r o x im a t e ly 60 f e e t t h ic k in th e m a p
a r e a , and c o n s i s t s of b r o w n to b u ff t h ic k - b e d d e d to m a s s i v e f in e - to
m e d iu m - g r a in e d c o m m o n ly p s e u d o b r e c c ia t e d s a c c h a r o id a l p e t r o lif e r o u s
d o lo m it e .
T h e m e m b e r i s g e n e r a lly a le d g e - f o r m in g u n it in t h is p a r t of
s o u th w e s t e r n M o n ta n a (M cM a rin is,
1964; S a n d b e r g ,
1965);'in th e m a p
a r e a , h o w e v e r , th e B ir d b e a r i s o n ly l o c a l l y le d g e - f o r m in g .
F e w f o s s i l s w e r e fo u n d in th e J e f f e r s o n of th e m a p a r e a , m a in ly
d u e to th e d o m in a n c e of d o lo m it e c o m p r is in g th e fo r m a tio n . . F o s s i l s
fou n d b y th e w r it e r in c lu d e A m p h ip or a a n d S tr o m a to p o r a .
The J e ffe r so n
i.s c o n s id e r e d to b e of L a te D e v o n ia n a g e b y m o s t m o d e r n w o r k e r s .
C o o p e r and o t h e r s (1 9 4 2 ) b e lie v e d th e f o r m a t io n to b e o f th e m id d le and
u p p e r F in g e r L a k e s s ta g e ; M cM a n n is (1 9 6 2 , p. 8) t e n t a t iv e ly id e n tifie d
f o s s i l s fr o m th e u p p e r b e d s of th e lo w e r m e m b e r w h ic h s u g g e s t th at
p a r t o f th e J e f f e r s o n m a y b e e q u iv a le n t t o u p p e r C h em u n g .
If s o , th e
u p p e r a g e li m i t o f th e f o r m a t io n in th e G a lla tin .R a n g e i s y o u n g e r than
th a t g iv e n b y C o o p e r an d o th e r s ( 19 4 2 ).
T h e f o s s i l s c o l le c t e d b y
M cM a n n is (1 9 6 2 ) a r e fr o m a n o u tc r o p 1-| m i l e s e a s t of th e s o u th e a s t
c o r n e r o f th e m a p a r e a .
25
T h r e e F o r k s F o r m a t io n
T h e T h r e e F o r k s F o r m a t io n c o n s i s t s o f th r e e m e m b e r s :
th e L o g a n .
G u lc h M e m b e r , th e T r id e n t M e m b e r , and th e S a p p in g to n M e m b e r
(S a n d b e r g ,
1965,.' p. N 10).
T h e s e n a m e s r e p la c e th e e v a p o r it ic m e m b e r ;
s h a le m e m b e r , an d S a p p in g to n S a n d sto n e M e m b e r , r e s p e c t i v e l y , o f
S a n d b e r g (1 9 6 2 ); th e y a l s o r e p la c e th e P o t la t c h M e m b e r , g r e e n sh a le
m e m b e r , and S a p p in g to n F o r m a t io n , r e s p e c t i v e l y , a s u s e d b y M cM a n n is
(1 9 6 2 ), and M c M a n n is and C h a d w ic k (1 9 6 4 ).
T h e fo r m a t io n i s c o m p r is e d of v e r y in c o m p e te n t m a t e r i a l in th e
m a p a r e a , fo r m in g g r a s s c o v e r e d s a d d le s ’ and s lo p e s .
A s a r e s u lt th e
s t r a t a a r e v e r y p o o r ly e x p o s e d and s u b d iv is io n of th e f o r m a t io n in to
m e m b e r s i s g e n e r a l ly im p o s s ib le .
T h ic k n e s s of th e f o r m a t io n r a n g e s
fr o m 40 f e e t to 60 f e e t , e x c e p t at one l o c a l i t y w h e r e it i s a b o u t 85 f e e t
th ic k .
-//
L o c a lly p r e s e n t a t th e b a s e of th e T h r e e F o r k s i s a th in u n it of o r a n g e
to b ro w n ir o n s to n e n o d u le s (I im o n ite ) in te r b e d d e d w ith p a le y e l lo w - g r e e n
th in -b e d d e d s h a ly and s a n d y d o lo m ite an d l i m e s t o n e . . S t r a t a h ig h e r in
th e fo r m a tio n c o n s i s t o f p a le y e llo w a n d ta n th in -b e d d e d s a n d y lim e s t o n e
and c a lc a r e o u s s a n d s to n e .
T h e in c o m p e te n t n a tu r e o f th e fo r m a tio n
s u g g e s t s th a t s h a le m a y c o n s t it u t e a m a j o r p a r t o f it.
A t th e m o u th of
S ou th C o tto n w o o d C a n y o n (NW 1 /4 NW 1 /4 s e c . 35, T . 3 5 , T . 35. , R.
5 E . ) 85 f e e t o f s t r a t a .o f th e L o g a n G u lc h M erh b er and p o s s i b l y the
b a s a l p a r t of th e T r id e n t M e m b e r i s e x p o s e d .
T h e s e s t r a t a c o n s is t of
l i g h t - y e l l o w - g r e e n th in -b e d d e d and f i s s i l e f in e l y m ic a c e o u s c a lc a r e o u s
26
an d d o lo m it ic sh ale and .g r a y - g r e e n r u b b ly li m e s t o n e , in te r s t r a t if ie d
w ith p in k t o ta n t h in - to m e d iu m - b e d d e d d o lo m it e , th a t a p p e a r s to b e
e x t e n s i v e l y w e a t h e r e d n e a r th e c o n t a c t w ith th e u n d e r ly in g J e f f e r s o n
F o r m a t io n .
T h e s h a le d e c r e a s e s u p w a r d in th e fo r m a t io n , w h e r e a s
th e d o lo m ite i s l e s s c o m m o n in th e b a s a l p a r t. - E ls e w h e r e in th e
m a p a r e a s t r a t a t y p ic a l o f the"S a p p in g to n a r e p r e s e n t and c o n s is t
o f y e llo w -b r o w n t h in -b e d d e d fin e g r a in e d c a lc a r e o u s q u a r tz s a n d s to n e .
A b la c k ,’ s h a le u n it c o m m o n ly p r e s e n t at th e b a s e of th e S a p p in g to n i s
n o t p r e s e n t in th e m a p a r e a , n o r i s it p r e s e n t to the so u th in the
■Garnet M ou n ta in q u a d r a n g le (M cM a n n is and C h a d w ick ,
1 964). . T he
b la c k s h a le (w h e r e p r e s e n t ) o v e r l i e s th e T r id e n t M e m b e r w ith r e g io n a l
d is c o n f q r m it y (S a n d b e r g ,
1 9 6 3 ).
W h ere th e b la c k s h a le i s a b s e n t th e
S a p p in g to n .and in p la c e s th e -L o d g e p o le L im e s t o n e o v e r l i e s th e -T r id e n t.
A t th e a b o v e l o c a l i t y (m o u th of- S ou th C o tto n w o o d C an yon ) th e
a n o m a l l o u s Iy t h ic k (85 fe e t ) L o g a n G u lch M e m b e r p o s e s a p r o b le m ;
W hy
sh o u ld Ijhe T r id e n t and S a p p in g to n -m em b er's b e a b s e n t in th e one p la c e
w h e r e Ijhe t h ic k n e s s of th e T h r e e F o r k s (to ta l) i s g r e a t e s t ?
The a n sw er
m a y b e r e l a t e d t o th e n o r m a lly b r e c c ia t e d n a tu r e of th e ■L o g a n .G u lc h and
l o c a lly - o f th e T r id e n t.
It i s p o s s i b l e th a t t h e s e tw o m e m b e r s r e p r e s e n t ,
s o lu tio n c o lla p s e b r e c c i a s , th e c o lla p s e p r o b a b ly o c c u r r in g due to th/e
in tr o d u c tio n o f g ro u n d w a te r d u r in g th e p o st-T r id e n fc ,. p r e -S a p p in g ton
e r o s io n in t e r v a l.
S u ch a p h e n o m e n o n c o u ld h a v e r e d u c e d th e t h ic k n e s s
of th e tyro .m e m b e r s to 4 0 - 5 0 f e e t ,, e x c e p t fo r -th e 85 fp o t th ic k d o lo m ite
u n it w h ic h w o u ld h a v e r e s i s t e d s o lu tio n .
It i s n o te w o r th y th a t t h is i s
27
th e o n ly l o c a l i t y (in th e m a p a r e a ) w h e r e th e m e m b e r ( s ) i s n e a r ly a ll
d o lo m ite .
. T h e d o lo m it e w o u ld h a v e b e e n a h ig h e r p o s it iv e a r e a d u rin g an y
p o s t - T r id e n t , p r e - L o d g e p o le L im e s t o n e e r o s io n tim e ; th u s th e
T r id e n t and S a p p in g to n m e m b e r s c o u ld h a v e b e e n s t r ip p e d off th e h ig h ,
b u t r e m a in e d e l s e w h e r e .
T h e T h r e e F o r k s r a n g e s fr o m L a te D e v o n ia n to e a r l i e s t M i s s is s ip p ia n
in a g e .
M c M a n n is and C h a d w ic k (1 9 6 4 , p . 10) s ta te th a t th e B ir d b e a r
M e m b e r of th e J e f f e r s o n F o r m a t io n a p p a r e n tly c o n ta in s u p p e r C h em u n g
e q u iv a le n t s ; t h e r e f o r e , th e b a s e of th e T h r e e F o r k s m a y b e l a t e s t
S e n e c a n or e a r l y C h a u ta u q u a n ( if th e J e f f e r s o n and T h r e e F o r k s a r e
\
c o n fo r m a b le ).
A c c o r d in g to S a n d b e r g (1 9 6 5 , p. NS) th e u p p e r m o s t p a r t
o f th e T h r e e F o r k s i s e a r l i e s t M i s s i s s i p p i a n ( e a r l i e s t K in d e r h o o k ia n ).
C o o p e r and o t h e r s (1 9 4 2 ) c o n s id e r e d th e T h r e e F o r k s to h a v e a v e r y
li m i t e d a g e r a n g e w ith in m i d - C a s s a d a g a n .
H o w e v e r , t h e ir d e fin itio n .
o f th e T h r e e F o r k s d id n o t in c lu d e th e S a p p in g to n .
M i s s is s ip p ia n
D a r k S h a le U n it
A d a r k s h a le u n it, p r e s e n t in n e a r b y a r e a s , i s n o t p r e s e n t w ith in th e
m ap area.
W h ere p r e s e n t , th e u n it o v e r l i e s th e S a p p in g to n M e m b e r o f
th e T h r e e F o r k s F o r m a t io n and u n d e r lie s th e L o d g e p o le L im e sto n e .
M c M a n n is (1 9 5 5 ) r e c o m m e n d e d th a t th e b la c k s h a le b e in c lu d e d a s p a r t
o f th e S a p p in g to n , w h ic h s o m e s u b s e q u e n t w o r k e r s h a v e d o n e .
W ith
28
f u r th e r f ie l d w o r k ,. h o w e v e r , M c M a n n is (1 9 6 2 ) n o ted th a t t h e u n it is
u n c o n fo r m a b le on th e S a p p in g to n and a p p e a r s l o c a lly to g r a d e u p w a rd
in to and b e c o n fo r m a b le w ith th e o v e r ly in g iilL o d g e p o le ; h e t h e r e f o r e
c o n s id e r e d it a s th e b a s a l u n it o f th e L o d g e p o le , a s h a v e s o m e o th er
w o r k e r s (e . g. , C o o p e r and S l o s s ,
1943; G u ts c h ic k and P e r r y ,
1959).
A c c o r d in g to S a n d b er g ' (1 9 6 5 ), h o w e v e r , c o r r e la t io n o f th e u n it in
M on tan a an d W y o m in g in d ic a t e s th a t it n o t o n ly un c o n fo r m a b ly o v e r l ie s
th e S ap p in g to n , b u t i s u n c o n fo r m a b ly o v e r la in b y th e L o d g e p o le , and
sh o u ld b e c o n s id e r e d a s a s e p a r a t e u n it.
T h e u n it i s p r e s e n t in n o r th e r n W y o m in g and s o u t h - c e n t r a l and
m u c h of w e s t e r n . M on tan a; it t h ic k e n s e a s t w a r d and s o u th e a s tw a r d fr o m
th e l o c a l r e g io n , w h e r e it v a r i e s fr o m O to 4 f e e t th ic k (S a n d b e r g , 1963).
T h e a b s e n c e o f th e s h a le u n it in th e m a p a r e a is n o t s u r p r is in g in v ie w
of th e p e r s i s t e n t p o s it iv e te n d e n c y of th e m a p a r e a , and th e f a c t th a t
th e u n it p in c h e s out in t h is p a r t of M o n ta n a .
It is q u ite p o s s i b l e th a t th e
b la c k s h a le m a y n e v e r h a v e b e e n d e p o s it e d in th e m a p a r e a . • S a n d b erg
(1 9 6 3 ) s t a t e s th a t th e b la c k s h a le u n it in s o u th w e s te r n M o n ta n a i s e n t ir e ly
o f E a r l y M i s s is s ip p ia n a g e - -K in d e r h o o k .
T h e o v e r ly in g L o d g e p o le
r a n g e s in a g e fr o m ab ou t m id d le K in d e r h o o k ia n to e a r l y O s a g ia n in th e
l o c a l r e g io n (S an d o and D u t r o,
I9 6 0 ).
S in c e th e s h a le u n it i s of e a r ly
K in d e r h o o k ia n a g e , a n y u n c o n fo r m ity th a t m a y be p r e s e n t m u s t r e p r e ­
s e n t a v e r y s h o r t le n g th o f t im e , and o n ly a v e r y s h o r t t i m e w o u ld be
a v a ila b le fo r e r o s io n o f th e s h a le .
H o w e v e r , th e u n it i s v e r y th in and
a s h o r t p e r io d of t im e m a y h a v e b e e n s u f f ic ie n t fo r r e m o v a l o f th e u n it.
29
■C o n v e r s e ly , th e w id e s p r e a d th in n a tu r e o f th e s h a le s u g g e s t s th a t th e
to p o g r a p h y of th e d e p o s it io n a l a r e a h a d v e r y li t t le r e l i e f and e r o s io n
sh o u ld h a v e b e e n v e r y s lo w .
. L o d g e p o le L im e s t o n e
v
T h e L o d g e p o le L im e s t o n e i s ab o u t 4 4 0
f e e t th ic k in th e m a p a r e a
and r e s t s d i s c o n fo r m a b ly on th e T h r e e - F o r k s . ^ C om m on ly th e L o d g e p o le
o v e r l i e s th e S a p p in g to n <M e m b e r of th e T h r e e F o r k s , b u t n e a r th e m o u th
o f S ou th C o tto n w o o d C a n y o n -(NW 1 /4 NW 1 /4 s e c . 3 5 ,, T . 35. ,. R . 5 E. ) .
t h e -S a p p in g to n i s a b s e n t and th e L o d g e p o le r e s t s on th e b a s a l p a r t o f th e
T r id e n t M e m b e r . . P r o b a b ly due t o ■c o m p e n s a t io n fo r th e in c r e a s e d th ic k ­
n e s s of th e T h r e e F o r k s a t t h is lo c a t io n (a s p r e v io u s ly n o ted ) th e L o d g e p o le i s -th in n er th a n e l s e w h e r e in th e m a p a r e a .
. T h e lo w e r o n e - t h ir d of th e - L o d g e p o le c o n s i s t s o f m e d iu m - g r a y ‘
l o c a l l y o r a n g e s ta in e d m e d iu m - to t h ic k - b e d d e d m o d e r a t e ly f o s s i l i f e r o u s
li m e s t o n e .
P r e s e n t in t h is p a r t of th e f o r m a t io n a r e z o n e s o f g r a y and
b r o w n c h e r t n o d u l e s ,. s t r i n g e r s , and l e n s e s , w h ic h te n d to b e - m a s s i v e
b u t in w h ic h f o r m e r b e d d in g p la n e s c a n c o m m o n ly b e d e lin e a t e d . . T he
u n it c o m m o n ly f o r m s l e d g e s . . S tr a ta of th e -m id d le o n e - t h ir d of the
fo r m a tio n , c o n s i s t o f y e llo w , oran ge., and g r a y th in -b e d d e d l o c a l l y c r o s s b e d d e d c o m m o n ly s h a ly a r g i lla c e o u s l i m e s t o n e , w ith in t e r s t r a t if ie d
g r a y - b r o w n m e d iu m - b e d d e d m i c r o c r y s t a l l i n e to c o a r s e l y c r y s t a llin e
li m e s t o n e .
T h e a r g i l l a c e o u s li m e s t o n e t y p ic a lly c o n ta in s w e ll p r e ­
s e r v e d f o s s i l s a s w e ll a s f o s s i l f r a g m e n t s , w h e r e a s th e in t e r s t r a t if ie d
l i m e s t o n e c o n ta in s m a in ly , f o s s i l f r a g m e n t s .
i
I
T h e u p p er o n e - t h ir d o f
30
th e fo r m a tio n c o n s i s t s o f o r a n g e - h r own' m e d iu m - and t h ic k -b e d d e d
l o c a l l y c r o s s - b e d d e d l i m e s t o n e , c o n ta in in g t h in - b e d s o f in t e r c a la t e d
b u ff c o lo r e d n o n - c a lc a r e o u s s h a le in th e lo w e r p a r t.
P r e s e n t in th e
m id d le p a r t of t h is u n it a r e t h ic k b e d s o f c o a r s e l y c r y s t a ll in e f o s s i l h a s h - l i m e s to n e . . T h e. c o n ta c t o f L o d g e p b le w ith th e o v e r ly in g M is s io n
C a n y o n . L im e s to n e i s s h a r p and c o n fo r m a b le .
The. L o d g e p o le i s of E a r l y M i s s is s ip p i a n a g e , r a n g in g ,f r o m m id d le
K in d e r h o o k ia n to e a r l y O s a g ia n (S a n d o -an d 'D u tr o,
I9 6 0 ).
M is s io n C an yo n . L im e s t o n e
T h e M is s io n C a n y o n L im e s t o n e c o n fo r m a b ly o v e r l i e s th e L o d g e p o le
an d i s a b o u t 375 f e e t t h ic k .
T h e b a s e of th e M is s io n C a n y o n .is c o n ­
s id e r e d to b e a t th e f i r s t o c c u r r e n c e o f a m a s s i v e li m e s t o n e u n it
im m e d ia t e ly o v e r ly in g t h in - to m e d iu m - b e d d e d s t r a t a o f t h e - L o d g e p o le .
T h e lo w e r p a r t o f th e M is s io n C a n y o n c o n s i s t s o f ta n li g h t - g r a y
w e a th e r in g t h ic k - b e d d e d an d m a s s i v e , l o c a l l y c r o s s - b e d d e d , f in e - to
c o a r s e - g r a i n e d l i m e s t o n e , w ith in te r s t r a t if ie d li g h t - g r a y to y e llo w b r o w n t h in - and m e d iu m - b e d d e d li m e s t o n e and d o lo m it ic l i m e s t o n e .
The
lo w e r p a r t c o m m o n ly c o n ta in s o o li t ic z o n e s , f o s s i l h a s h , and lo c a lly
w e ll p r e s e r v e d f o s s i l s .
T he u p p e r p a r t o f th e f o r m a t io n i s c h a r a c t e r iz e d b y li m e s t o n e s im il a r
■to th a t o f th e lo w e r p a r t, b u t th e in te r s t r a t if ie d b e d s a r e m a in ly d o lo m it e .
T h e d o lo m ite i s p r in c ip a lly o f t h r e e t y p e s , l i s t e d in o r d e r o f d e c r e a s in g
a b u n d a n ce:
(I ) g r a y - b r o w n th in -b e d d e d to m a s s i v e fin e - t o m e d iu m ­
g r a in e d d o lo m it e , (2) li g h t - t a n w h ite w e a th e r in g t h in - to m e d iu m - b e d d e d
31
d e n s e d o l o m i t e ,. and (3) b r o w n t h ic k - b e d d e d f in e - g r a i n e d s a c c h a r o id a l
p e t r o li f e r o u s d o lo m it e , id e n t ic a l to th a t o f th e J e f f e r s o n . . R o b e r ts (1 9 6 1 ,
p. B 2 9 4 ) b e l i e v e s th e d o lo m it e to h a v e b e e n d e p o s it e d d i r e c t l y fr o m s e a
w a te r ; h is r e a s o n in g i s b a s e d on (I) th e in t im a t e in t e r la y e r in g of d o lo m ite
an d li m e s t o n e , (2) th e f in e r c r y s t a ll in it y of th e d o lo m it e s a s o p p o se d to
th a t of th e l i m e s t o n e s , and (3) a l a r g e r c o n te n t of in s o lu b le r e s id u e s in
i
th e d o lo m it e s .
H o w e v e r , d o lo m it iz e d f o s s i l f r a g m e n t s s u g g e s t th a t
d o lo m it iz a t io n i s a s e c o n d a r y f e a t u r e .
G r a y and b r o w n c h e r t ' l e n s e s , n o d u le s , an d s t r in g e r s a r e abundant
in th e u p p e r p a r t of th e f o r m a t io n , b u t a r e l e s s c o m m o n in th e lo w e r
p a r t.
S o m e of th e c k e r t n o d u le s an d s t r in g e r s c o n ta in s i l i c i f i e d f o s s i l s ,
n o ta b ly s o lit a r y c o r a l s .
S o lu tio n o r c o l la p s e b r e c c i a s a r e c o m m o n in th e u p p e r p a r t of th e
fo r m a t io n and a r e o f tw o ty p e s :
c o n tin u o u s z o n e s .
(I) ir r e g u la r m a s s e s , and (2) l a t e r a lly
T h e ir r e g u la r m a s s e s o f b r e c c ia o c c u r h ig h e r in th e
fo r m a tio n th a n th e l a t e r a l l y c o n tin u o u s b r e c c i a z o n e s and m a y h a v e s e r v e d
a s c o n d u its to th e l a t e r a l l y c o n tin u o u s b r e c c i a .
T h e l a t e r a l l y co n tin u o u s
b r e c c i a c o m m o n ly w e a t h e r s b lu is h - g r a y and c o n s is t s o f f r a g m e n te d d e n s e
b r o w n d o lo m it e , w ith a fe w ir r e g u la r c h e r t z o n e s .
It i s l o c a l l y c e m e n te d
w ith y e llo w or r e d c a l c a r e o u s m u d s to n e , t y p ic a l of th a t of th e A m s d e n
F o r m a t io n .
K le p p e r and o t h e r s (1 9 5 7 , p . 20) b e lie v e th e b r e c c i a fo r m e d
" d u rin g a p o s t - M i s s i o n C a n y o n p r e - A m s d e n e r o s io n in t e r v a l b y'-p en ec o n te m p o r a n e o u s f o r m a t io n and c o lla p s e of s o lu tio n c a v e r n s . " M id d le to n
(1 9 6 1 ) a l s o b e l i e v e s th e b r e c c i a i s a s o lu t io n a n d c o lla p s e f e a t u r e , but d id
32
n o t for m, p e n e c o n t e m p o r a n e o u s ly (o r b y m e t a s o m a t ic r e p la c e m e n t
o r b y r e c r y s t a ll iz a t i o n ) .
T h e M i s s io n C a n y o n i s o f la t e E a r ly to e a r ly L a te M i s s is s ip p ia n
a g e (la te O s a g e and e a r l y M e r a m e c ) ( R o b e r t s ,
an d D u tr o,
I 9 6 0 , p.
196,1, p. B 294; S ando
1 1 7 -1 2 3 ).
B ig S n o w y G roup
T h e B ig S n o w y G rou p i s n ot p r e s e n t in th e m a p a r e a , and th e n e a r e s t
k n ow n o c c u r r e n c e o f th e g r o u p i s to th e n o r th in th e B r id g e r R a n g e .
In
t h i s r a n g e d e fin it e B ig 'S n o w y s t r a t a a r e p r e s e n t a s fa r so u th a s B r id g e r
P e a k , and a p p a r e n tly a r e - a b s e n t in th e s o u th e r n p o r tio n of th e ra n g e
(M c M a n n is ,
19 5 5 , p . 1 4 0 3 ).
T h e s t r a t a a p p e a r t o p in c h out a t o r n e a r
B r id g e r P e a k , b u t th e r o c k s d o n o t s u g g e s t s h o r e li n e c o n d itio n s ,(p e r s o n a l
c o m m u n ic a t io n ,. W. J. M c M a n n is,
1 9 6 5 ).
T h is s u g g e s t s tha.t th e B ig
' S n o w y w a s o n c e -m o r e w id e s p r e a d , q u ite p o s s i b l y in c lu d in g th e m ap, a r e a ,
an d w a s r e m o v e d b y p o s t^ B ig S n ow y, p r .e -A m s d e n e r o s io n .
,
M i s s i s s i p p i a n and P e n n s y lv a n ia n
. A m s d e n F o r m a tio n
S tr a ta o f th e A m s d e n F o r m a t io n r a n g e fr o m 49 f e e t to 78 f e e t th ic k in
th e m a p a r e a .
T h e f o r m a t io n d i s c o n f o r m a b ly o v e r l i e s th e M is s io n C a n y o n
. an d i s g e n e r a l ly b e li e v e d t o h a v e b e e n d e p o s it e d on k a r s t to p o g r a p h y .
A m s d e n f o r m s s t e e p s lo p e s but ,o u tc r o p s a r e p o o r .
The
33
T h e A m s d e n c o n s i s t s o f p u r p lis h t h in - to m e d iu m -b e d d e d d o lo m it ic
l i m e s t o u e , y e llo w t o w h ite th in - to m e d iu m - b e d d e d c a l c a r e o u s m u d s to n e ,
b u ff c o lo r e d th in -b e d d e d rp ,ed iu m - to c o a r s e - g r a i n e d p o r o u s lim e s t o n e ,
an d a r e d ,, g r a y , arid b la c k c h e r t y d o lo m it e z o n e .
T he u p p erm o st
A m s d e n c o n s i s t s o f ta n and p u r p le m o t t le d th in -b e d d e d s i l t s to n e w h ich
i s o v e r la in b y y e l l o w - g r a y t h in - to m e d iu m -b e d d e d m e d iu m - to c o a r s e ­
g r a in e d an d g e n e r a l ly p o o r ly in d u r a te d s a n d y d o lo m it e , th a t g r a d e s u p ­
w a r d in to t y p ic a l Q u a d ra n t Q u a r tz ite .
T h e A m s d e n - Q u ad ran t c o n ta c t
w a s c h o s e n a t th e to p o f th e h ig h e s t r e d s tr a tu m b e tw e e n th e M is s io n
C a n y o n c a r b o n a t e s and t y p ic a l Q u a d ra n t s a n d s to n e .
R ed s t r a t a a r e p r e s e n t w h e r e v e r th e A m s d e n i s p r e s e n t , w ith th e
e x c e p t io n o f on e lo c a lit y . .'A t t h is lo c a tio n (o n Sou th C o tto n w o o d C r e e k )
th e fo r m a tio n i s v e r y f a in t ly p in k to w h it e , th e u s u a l r e d c o lo r p o s s i b l y
h a v in g b e e n le a c h e d b y g ro u n d w a t e r .
If s o , th e m o v e m e n t o f th e w a te r
w a s not d o w n w a rd a s th e s o lu tio n b r e c c i a s o f th e u n d e r ly in g M is s io n
C a n y o n a r e n o t s ta in e d t h e ir c h a r a c t e r i s t i c r e d c o lo r .
R e c e n t p a le o n t o lo g ic s t u d ie s in th e g e n e r a l r e g io n o f th e m a p a r e a
in d ic a te th a t th e A m s d e n is o f L a te M i s s is s ip p ia n and E a r l y P e n n s y lv a n ia n
a g e (R o b in so n ,
19 6 3 , p. 4 8 - 4 9 ) .
Q u a d ra n t Q u a r tz ite
T h e Q u a d ra n t Q u a r tz ite .c o n fo r m a b ly o v e r l i e s th e A m s d e n and d i s c o n fo r m a b ly u n d e r lie s the. S a w to o th F o r m a t io n ( J u r a s s i c ) .
C o m p le te
s e c t io n s of th e Q u a d ra n t a r e p r e s e n t o n ly in Sou th C o tto n w o o d C an yon
w h e r e th e f o r m a t io n c r o p s ou t on th e n o r t h e a s t s id e of th e c r e e k .. In
34
t e r m s o f t h ic k n e s s , th e Q u a d ra n t i s th e m o s t v a r ia b le f o r m a t io n in th e
m a p a r e a ; it r a n g e s fr o m 198 f e e t th ic k in th e NW 1 /4 SE 1 /4 s e c . I,
T . 4S. ,. R . BE. , to a p p r o x im a t e ly 300 f e e t th ic k in th e N E 1 /4 SE 1 /4
sec.
35 , T . 35. , R . S E . - - a d is t a n c e of o n ly o n e .m ile .
f
T h e v a r ia tio n
i s a ttr ib u te d to p o s t -Q u a d r a n t - p r e -S a w to o th e r o s io n .
T h e lo w e r p a r t of th e Q uaclrant ’c o n ta in s ta n and y e l lo w - g r a y m e d iu m an d th ic k -b e d d e d f i n e - to m e d iu m - g r a in e d d o lo m it e in te r b e d d e d w ith
y e llo w and w h ite m e d iu m - g r a in e d q u a r tz s a n d s to n e .
a r e p r o g r e s s i v e l y f e w e r and th in n e r u p s e c t io n .
T h e d o lo m ite b e d s
T h e m a j o r p a r t of th e
f o r m a tio n i s ta n to w h ite m e d iu m and t h ic k - b e d d e d fin e - to .m e d iu m g r a in e d l o c a l l y c r o s s - b e d d e d q u a r tz s a n d s t o n e .
T he s a n d s to n e i s
g e n e r a l ly m o d e r a t e ly in d u r a te d b u t i s l o c a l l y q u a r t z it ic .
L o c a lly i n t e r ­
b e d d e d in th e u p p e r 25 f e e t o f th e f o r m a t io n a r e th ic k b e d s of y e llo w -
'
w h ite f in e - to m e d iu m - g r a in e d c a lc a r e o u s q u a r tz s a n d s to n e c o n ta in in g
g r a y c h e r t n o d u le s and s t r in g e r s ; l e s s c o m m o n ly p r e s e n t i s m e d iu m b e d d e d d o lo m it e .
T h e Q u a d ra n t c o m m o n ly f o r m s t a lu s c o m p r is e d of
r e c t a n g u la r b lo c k s .
The
Q u a d ra n t h a s y ie ld e d v e r y f e w f o s s i l s in th e r e g io n , b u t th e
f o r m a tio n i s g e n e r a l ly c o n s id e r e d to b e o f P e n n s y lv a n ia n a g e .
P e r m ia n
P h o s p h o r ia F o r m a t io n
S tr a ta of th e P h o s p h o r ia
F o r m a t io n a r e n o t p r e s e n t in th e m a p a r e a .
T o th e so u th in th e a d ja c e n t G a r n e t M o u n ta in q u a d r a n g le th e fo r m a tio n
35 th in s fr o m 119 f e e t in th e s o u th w e s t e r n c o r n e r of th e q u a d r a n g le to
105 f e e t on S q u aw C r e e k in th e n o r t h e a s t e r n p a r t (M cM a n n is and
C h a d w ick ,
1964 , p.
14), and i s b e tw e e n 75 f e e t and 100 f e e t th ic k 1-|
m i l e s e a s t of th e s o u th e a s t c o r n e r of th e m a p a r e a ( W. M . W eb er,
U npub. M a s te r o f S c ie n c e T h e s i s , M o n ta n a S ta te U n iv . , B o z e m a n ,
p. 2 5 ).
1965,
A t R o c k y C a n y o n ab ou t 12 m i l e s to th e n o r t h - n o r t h e a s t , th e
P h o s p h o r ia i s o n ly .36 f e e t t h ic k ( C r e s s m a n and S w a n so n ,
1964, p. 305)
an d i s a b s e n t 6 m i l e s f a r t h e r n o r th in th e s o u th e r n en d o f th e B r id g e r
•R a n g e (M c M a n n is,
1955, p.
1404).
T h e p r e s e n t e d g e of th e P h o s p h o r ia i s m o s t li k e ly n o t th e -d e p o s itio n a l e d g e , b u t th e la t t e r m a y n o t h a v e b e e n v e r y fa r f r o m th e p r e s e n t
e d g e o f th e fo r m a tio n .
A v q r y im p o r ta n t f a c t o r in t h is r e g a r d i s th e
le n g t h 'o f t im e th a t the' f o r m a t io n w a s e x p o s e d to e r o s io n .
T h e s tr o n g
p o s s i b i l i t y e x i s t s th a t L o w e r T r i a s s i c s t r a t a w e r e o n ce p r e s e n t in the
m ap a r e a (s e e T r ia s s ic ).
T h e d u r a tio n o f th e P h o s p h o r ia e r o s io n , th en ,
i s d e p e n d e n t on (I ) th e t h ic k n e s s and e x t e n t o f th e p o s tu la t e d L o w e r
T r i a s s i c s t r a t a , a n d (2) th e a m o u n t of t im e n e c e s s a r y to cu t th ro u g h th e
T r i a s s i c s t r a t a ( r a te o f e r o s io n ) .
M cM a n n is and C h a d w ick (1 9 6 4 ) n o te th a t th e lo w e r u n it o f th e P h o s p h o r ia
in th e G a r n e t M o u n ta in q u a d r a n g le c o n ta in s p r o g r e s s i v e l y m o r e q u a r tz ite
f r o m so u th to n o r th (to w a r d th e m a p a r e a ); th e u p p e r u n it o f th e f o r m a tio n
i s n e a r ly a l l q u a r tz ite and c o n ta in s ab u n d an t b u r r o w s t r u c t u r e s .
The
b u r r o w s t r u c t u r e s a r e c o n fin e d to p la t f o r m s e d im e n t s and in d ic a te th a t
th e b u r r o w in g a n im a ls w e r e of s h a llo w - w a t e r h a b ita t ( C r e s s m a n and
36
S w a n s o n , 1 9 6 4 , p. 3 5 1 - 3 5 4 ) .
T h is s u g g e s t s th a t th e d e p o s it io n a l s e a
w a s s h a llo w an d p o s s i b l y n e a r a s h o r e lin e .
T h e in c r e a s e in q u a r tz ite
,
to w a r d th e m a p a r e a s u g g e s t s th a t th e m a p a r e a m a y h a v e b e e n p o s it iv e
during" a t l e a s t p a r t of P h o s p h o r ia t im e and s u p p lie d th e m a t e r i a l fo r th e
q u a r tz ite (p r o b a b ly d e r iv e d fr o m th e Q u ad ran t Q u a r tz ite ).
In v ie w o f th e
f a c t th a t a l l o f th e f o r m a t io n s in th e m a p a r e a a r e th in n e r th a n t h o s e of
th e G a r n e t M o u n ta in q u a d r a n g le , it i s p o s s i b l e th a t th e P h o s p h o r ia w a s
n e v e r d e p o s it e d in th e m a p a r e a .
A s p r e v i o u s ly m e n t io n e d , th e r e e x i s t s
th e e q u a lly p r o b a b le a lt e r n a t iv e th a t P h o s p h o r ia s t r a t a w e r e d e p o s ite d
in and s u b s e q u e n t ly r e m o v e d fr o m th e m a p a r e a .
A m o r e p o s it iv e a n s w e r
a w a it s a d e t a ile d stu d y of th e P h o s p h o r ia in th e n o r th en d o f th e G a lla tin
R ange.
T r ia s s ic
~,
T r i a s s i c s t r a t a a r e a b s e n t in th e m a p a r e a but a r e p r e s e n t n e a r b y .
T h e T r i a s s i c of s o u th w e s t e r n M o n ta n a i s r e p r e s e n t e d b y th e fo llo w in g
s e q u e n c e of L o w e r T r i a s s i c fo r m a t io n s :
th e m a r in e D in w o o d y F o r m a t io n
w h ic h in te r to n g u e s w ith , and i s o v e r la in b y , th e r e d b e d W o o d sid e or
C h u g w a ter F o r m a t io n , w h ic h in tu rn i s o v e r la in b y th e m a r in e T h a y n e s
F o r m a t io n w h e r e th e la t t e r i s p r e s e n t (K u m m e l,
I9 6 0 ; M o r it z ,
1951).
T h e n e a r e s t o c c u r r e n c e o f D in w o o d y i s 15 m i l e s so u th of t h e m a p a r e a
w h e r e M c M a n n is and C h a d w ick (1 9 6 4 ) m e a s u r e d 265 f e e t o f s t r a t a .
D in w o o d y s t r a t a a r e a l s o r e p o r t e d in th e M a d is o n R a n g e , w e s t of th e m a p
a r e a (M o r itz ,
1 9 5 1 ).
T h e W o o d sid e i s p r e s e n t a p p r o x im a t e ly 40 m i l e s
37
so u th of th e m a p a r e a w h e r e it o v e r l i e s th e D in w o o d y and h a s a m in im u m
t h ic k n e s s of 350 f e e t (W itk in d ,
p o s s ib ly be
1964).
W itk in d a l s o m a p p e d w h a t m a y
a 9 - f o o t t h ic k s e c t io n of th e T h a y n e s .
N o o th e r T h a y n e s -
s t r a t a h a v e b e e n r e p o r t e d in th e v ic in it y of th e m a p a r e a an d , in
M o n ta n a , a r e a p p a r e n t ly r e s t r i c t e d to th e s o u t h w e s t e r n m o s t p a r t of
th e s t a t e .
M o r i t z .(195 I, p.
1798) s t a t e s th a t M id d le and U p p e r T r i a s s i c
s t r a t a a r e n ot p r e s e n t in s o u th w e s t e r n M o n ta n a and th a t t h e r e i s "no
e v id e n c e to in d ic a t e th a t t h e y w e r e e v e r d e p o s it e d . "
M o r itz (1 9 5 1 ) s t a t e s th a t th e s i l t s t o n e s of th e D in w o o d y a r e of th e
s u b g r a y w a c k e ty p e and a r e t h e r e f o r e s u g g e s t i v e o f m il d l y u n s ta b le c o n ­
d itio n s ; t h is m a y r e f l e c t in c r e a s i n g s u b s id e n c e of th e s h e lf and c o n s e q u e n tly
in u n d a tio n of a la r g e r a r e a .
T h e D in w o o d y of th e G a r n e t M o u n ta in q u a d ­
r a n g le i s n ot t y p ic a l o f a s h o r e lin e d e p o s it; it i s p o s s i b l e , t h e r e f o r e , th a t
th e fo r m a tio n w a s o n c e m o r e w id e s p r e a d ( p o s s i b l y c o v e r in g th e m a p a r e a )
an d w a s s u b s e q u e n t ly r e m o v e d b y e r o s io n .
T h e lo n g p o s t - E a r l y T r ia s s i c ,
p r e - M id d le J u r a s s i c h ia t u s ( a p p r o x im a t e ly 50 m . y. ) w o u ld h a v e b e e n
s u f f ic ie n t t im e to r e m o v e T r ia s s i c s t r a t a fr o m th e m a p a r e a .
J u r a s s ic
J u r a s s ic
s t r a t a a r e c o n fin e d to th e e a s t - c e n t r a l p a r t o f th e m a p a r e a
w h e r e th e y c r o p out on th e e a s t w a ll o f S ou th C o tto n w o o d C a n y o n .
The
m a r in p E l l i s G ro u p , in c lu d in g th e S a w to o th , R i e r don, an d S w ift f o r m a t io n s ,
an d th e n o n - m a r in e M o r r is o n F o r m a t io n to g e t h e r c o m p r is e th e 403 -fo o t
J u r a s s ic seq u en ce.
I
38
S a w to o th F o r m a t io n
T he S a w to o th F o r m a t io n i s 82 f e e t t h ic k in th e m a p a r e a and d is c o n fo r m a b ly o v e r l i e s the Q u ad ran t F o r m a t io n ,
A t th e b a s e o f th e
S a w to o th o c c u r s a g r a y to d a r k b ro w n c o n g lo m e r a t ic s a n d s to n e , c o m ­
p r i s e d o f m a r o o n , ,g ra y , and b la c k su b a n g u la r to su b r o u n d ed c h e r t
p e b b le s and lig h t g r a y li m e s t o n e p e b b le s in a m a t r ix of q u a r tz and c h e r t
san d .
T h e u n it i s ir r e g u l a r l y thin-.
U p w a r d , a p p r o x im a t e ly 25 f e e t of
I
th in -b e d d e d f o s s i l i f e r o u s c a r b o n a c e o u s s i l t sto n e and d o lo m it e a r e
p r e se n t.
T h e m a j o r o v e r ly in g p o r tio n o f th e fo r m a t io n i s c o m p r is e d of
52 f e e t of lig h t g r a y th in -b e d d e d b lo c k y , h a c k ly , or s h a ly a b u n d a n tly
f o s s i l i f e r o u s li m e s t o n e .
T h e u p p e r m o s t fe w f e e t o f th e f o r m a t io n c o n s i s t s
o f y e llo w -b r o w n f o s s i l i f e r o u s m u d s to n e .
. E a s t o f th e m a p a r e a R o b e r t s (1 9 6 4 ) m a p p e d e q u iv a le n t s t r a t a and
t e r m e d th e s e q u e n c e th e P ip e r F o r m a t io n , th e c e n tr a l and e a s t e r n M o n tan a
a g e e q u iv a le n t of th e S a w to o th .
H o w e v e r , h is lit h o lo g ic d e s c r ip t io n i s
v e r y s im il a r to th a t of th e w r it e r , an d -d iffe r s v e r y s ig n if ic a n t ly fr o m th a t
o f th e P i p e r a t th e ty p e s e c t io n a s d e fin e d b y I m la y and o t h e r s (1 9 4 8 ) and
e x p a n d e d b y N o r d q u is t (1 9 5 5 ) to in c lu d e m e m b e r s ta tu s fo r c e r t a in u n its .
T h e f o r m a tio n in th e tw o m a p a r e a s a r e c l o s e l y s im il a r to th a t o f th e
S a w to o th in th e ty p e E l l i s s e c t io n s a s d e s c r ib e d b y C ob b an (1 9 4 5 , p . 12 7 2 1 2 7 3 ).
T h e S a w to o th i s of M id d le J u r a s s i c a g e , and in c lu d e s th e B a jo c ia n
an d B a th o n ia n s t a g e s (M cK ee and o t h e r s , 1 9 5 6 , p. 5 ).
39
R ie r d o n F o r m a tio n .
T h e R ie r d o n F o r m a t io n , m id d le u n it o f th e E l l i s G ro u p , i s 5 I f e e t
t h ic k in th e m a p a r e a and r e s t s c o n f o r m a b ly o±i th e S a w to o th .
The
f o r m a tio n c o n s i s t s of a b a s a l lig h t g r a y w e a th e r in g ta n m e d iu m - b e d d e d
d e n s e ly o o li t ic li m e s t o n e .
U p w a rd , th e R ie r d o n b e c o m e s t h ic k -b e d d e d
an d m a s s i v e and c o n s i s t s o f a le d g e f o r m in g g r a y - b r o w n w e a th e r in g
f o s s i l - f r a g m e n t e d o o li t ic li m e s t o n e .
T h e la t t e r u n it w e a t h e r s to a
p itte d s u r f a c e and l o c a l l y c o n ta in s b r o w n c h e r t f r a g m e n t s and th in
s t r i n g e r s a t w h a t a r e o b v io u s ly f o r m e r b e d d in g p la n e s .
l o c a l l y p r e s e n t on n o n - c h e r t y b e d d in g p la n e s .
S t y lo li t e s a r e
T h e s u r f a c e o f th e top
m o s t b e d o f th e R ie r d o n i s v e r y u n e v e n , and lim o n it e an d h e m a t it e d e ­
p o s it s a r e c h a r a c t e r i s t i c of it.
T h e S w if t - R ie r d o n c o n ta c t i s m a r k e d ly
1
ir r e g u la r ( d is c o n f o r m a b le ) ; c o n s e q u e n tly , t y p ic a l u p p er R ie r d o n s t r a t a
,
-
,
c o n s is t in g of g r a y - g r e e n th in ly la m in a t e d f o s s i l i f e r o u s li m e s t o n e and
l e s s c o m m o n ly n o d u la r li m e s t o n e a r e o n ly lo c a lly p r e s e n t .
T h ese
s t r a t a do n o t e x c e e d th r e e f e e t in t h ic k n e s s .
T h e R ie r d o n i s of la t e M id d le J u r a s s i c a g e ( e a r ly t o m id d le C a llo v ia n )
(M c K e e and o t h e r s ,
19 5 6 , p. 5).
S w ift F o r m a t io n
T h e S w ift F o r m a t io n i s 58 f e e t th ic k in th e m a p a r e a and o v e r l ie s th e
R ie r d o n w ith a m a r k e d d i s c o n fo r m ity .
T h e b a s a l p a r t o f th e fo r m a tio n co n
g i s t s o f g r a y t h ic k - b e d d e d m e d iu m g r a in e d lin o n it ic c a l c a r e o u s q u a rtz
s a n d s to n e th a t i s o n ly l o c a l l y p r e s e n t .
It i s o v e r la in b y 10 f e e t of d a r k
b r o w n to b la c k m e d iu m - an d th ic k - b e d d e d , c r o s s - b e d d e d m e d iu m g r a in e d
40
s p a r in g ly g la u c o n it ic n o n - c a lc a r e o u s q u a r tz s a n d s to n e .
R ip p le .m a r k s a r e
p r e s e n t on s o m e b e d s and d if f e r e n t ia l w e a th e r in g h a s c a u s e d s o m e o f th e
c r o s s - b e d s to s^and out in r e l i e f .
G r a y , g r e e n , and b la c k su b a n g u la r
c h e r t p e b b le s a r e s p o r a d ic a lly p r e s e n t in th e u n it.
T h e r e m a in d e r of
th e S w ift c o n s i s t s o f 45 f e e t of ta n l o c a l l y m a r o o n s t a in e d m e d iu m - and
t h ic k -b e d d e d s p a r in g ly c r o s s - b e d d e d lim o n it ic m o d e r a t e ly in d u r a te d
c a l c a r e o u s s a n d s to n e ; n e a r th e to p of th e u n it a r e a fe w in t e r s t r a t if ie d
b e d s o f lig h t b lu e - g r a y sa n d y and s h a ly l i m e s t o n e .
T h e e r o s io n a l u n c o n f o r m it y a t th e R ie r d o n - S w if t c o n ta c t (Im Jay and
o th e r s,
19.48; Im la y ,
1956) i s a t t e s t e d to b y th e m a r k e d ly ir r e g u la r c o n ­
t a c t and th e s p o r a d ic p r e s e n c e of th e u p p e r R ie r d o n s h a le in th e m a p a r e a ,
an d th e p e r s i s t e n t p r e s e n c e o f th e la t t e r to th e e a s t and i t s a b s e n c e to th e
so u th .
'
T h e S w ift i s of e a r l y to m id d le L a te J u r a s s i c a g e (O x fo r d ia n ) and th e
. h ia t u s r e p r e s e n t s th e u p p e r on e - h a lf o f th e C a llo v ia n (M c K e e and o t h e r s ,
, 1956,
p.
5 ).
M o r r is o n F o r m a t io n
S tr a ta o f th e n o n - m a r in e M o r r is o n F o r m a t io n o v e r l i e an d a r e m a r k e d ly
d if f e r e n t fr o m t h o s e o f th e S w ift; th e le d g e - f o r m in g sa n d y li m e s t o n e or
s a n d s to n e of th e m a r in e S w ift c h a n g e s u p w a rd to d e e p r e d c la y s to n e of th e "
n o n - m a r in e M o r r is o n .
I m la y (1 9 5 6 , p. 5 6 5 ) s t a t e s th a t n o e v id e n c e h a s
b e e n fou n d fo r a d i s c o n f o r m it y at t h is con tact,;
t h ic k in th e m a p a r e a and i s p o o r ly e x p o s e d .
T h e M o r r is o n i s 212 f e e t
41
T h e lo w e r o n e - h a lf o f th e fo r m a t io n c o n s i s t s of r e d d is h - b r o w n
m u d s to n e an d s h a le w ith in t e r s t r a t if ie d r e d - g r a y th in -b e d d e d f i n e ­
g r a in e d h a r d c a lc a r e o u s q u a r tz s a n d s to n e an d s ilt s t o n e , f in e - g r a in e d
n o n - c a lc a r e o u s li m o n i t ic and h e m a t it ic q u a r tz s a n d s t o n e ,. and th in d i s ­
c o n tin u o u s b e d s o f lig h t g r e e n and g r a y n o d u la r li m e s t o n e .
T h e u p p er
o n e - h a lf of th e M o r r is o n c o n ta in s lig h t g r e e n th in -b e d d e d s a n d y lim e s t o n e
in th e lo w e r p a r t, b u t th e u n it i s d o m in a te d b y ta n to g r a y t h in - and m e d iu m b e d d e d lim o n it ic c a l c a r e o u s f in e - g r a i n e d q u a r tz s a n d s to n e and s ilt s t o n e .
T h e s a n d s to n e and s i l t s t o n e a r e l o c a l l y c r o s s - b e d d e d and a r e p o o r ly to
w e ll in d u r a te d .
P la n t f r a g m e n t s w e r e fou n d in th e u p p e r b e d s o f th is
u n it.
I m la y and o t h e r s (1 9 4 8 ) c o n s id e r th e M o r r is o n t o b e o f L a te J u r a s s i c
a g e , r a n g in g fr o m e a r l y K im m e r id g ia n th r o u g h e a r l y P o r tla n d ia n .
C r e t a c e ou s
C r e t a c e o u s s t r a t a a r e p r e s e n t o n ly in th e e a s t - c e n t r a l p a r t of th e m a p
a r e a , h ig h on th e e a s t s id e o f S o u th C o tto n w o o d C r e e k .
T hey are r e p r e ­
s e n te d b y 250 f e e t o f S e d im e n ta r y r o c k s o f th e K o o te n a i an d T h erm O p p lis
f o r m a t io n s . . A t h ic k e r s e q u e n c e o f t h e s e s t r a t a (a b ou t 700 fe e t ) i s r e ­
p o r te d b y M c M a n n is and C h a d w ick (1 9 6 4 ) 10 m i l e s s o u th w e s t of th e a b o v e
lo c a t io n , an d th ick er, s e q u e n c e s of t h e s e an d yo u n g er' C r e t a c e o u s s t r a t a
a r e p r e s e n t n e a r H y a lit e Re s e r v o i r a b o u t tw o m i l e s s o u t h e a s t of th e m a p
a r e a (4 0 0 0 fe e t ) ( R o b e r t s ,
(M c M a n n is,
1 9 6 4 ), th e B r id g e r R a n g e (1 0 ,0 0 0 fe e t )
1955); and n e a r L iv in g s t o n , M on tan a ( 1 2 ,0 0 0 f e e t ) ( R o b e r t s ,
42
1 9 6 5 ).
T h e a b s e n c e of th e y o u n g e r C r e t a c e o u s r o c k s .in th e -m ap a r e a
i s d ue t o (I ) r e c e n t e r o s io n , (2) fa u ltin g and e r o s io n p r io r to d e p o s i­
tio n of T e r t i a r y v o lc a n ic r o c k s , and (3) p r o b a b ly in p a r t n o n - d e p o s i­
tio n .
R o b e r t s (1965)' h a s c o r r e la t e d th e C r e t a c e o u s (and L o w e r T e r t ia r y )
r o c k s o f t h is r e g io n w ith t h o s e of o th e r a r e a s of M o n ta n a an d W y o m in g .
In s o d o in g h e e le v a t e d th e L iv in g s t o n an d C o lo r a d o f o r m a t io n s to g ro u p
r a n k , th e l a t t e r f o r m a t io n h a v in g lo n g h a d t h is s ta tu s in v a r io u s a r e a s .
H e th e n a p p lie d f o r m a t io n n a m e s to th e c o r r e la t e d u n its a n d d e s ig n a t e d
m e m b e r s ta tu s fo r c e r t a in lit h o lo g ic s u b d iv is io n s of th e f o r m a t io n s .
K o o te n a i F o r m a t io n
T h e K o o te n a i F o r m a t io n i s a t r ip a r t i t e s e q u e n c e Of n o n - m a r in e s t r a t a
d i s c o n fo r m a b ly o v e r ly in g th e M o r r is o n .
T h e fo r m a tio n i s 205 f e e t th ic k
w h e r e m e a s u r e d in S o u th C o tto n w o o d CanyOn.
i
T h e b a s a l u n it o f th e K o o te n a i, th e s o c a lle d P r y o r C o n g lo m e r a te
M e m b e r of R o b e r t s (1 9 6 5 ), i s 45 f e e t th ic k .
It c o n s is t s of lig h t g r a y , ta n ,
an d p in k t h ic k -b e d d e d to m a s s i v e c r O s s - b e d d e d m e d iu m - and c o a r s e ­
g r a in e d to c o n g lo m e r a t ic s a n d s to n e .
T h e s a n d s to n e is o f th e s a lt and
p e p p e r ty p e , b e in g c o m p r is e d o f su b a n g u la r to sub ro u n d ed g r a in s o f ta n
a n d w h ite q u a r tz an d b la c k c h e r t .
S u b r o u n d ed and r o u n d e d w hite* ta n ,
g r a y , p u r p le , and b la c k c h e r t p e b b le s and r a r e l y q u a r tz ite p e b b le s c o m ­
p r i s e th e c o n g lo m e r a t ic p a r t of th e s a n d s to n e .
L o c a lly th e s a n d s to n e i s
p o o r ly in d u r a te d a n d d o e s n o t f o r m p r o m in e n t o u t c r o p s .
43
T h e m id d le u n it o f th e K o o t e n a i'is 130 f e e t th ic k , and i t s u n ity l i e s
in th e f a c t th a t it i s 'c o m p r is e d of m a n y d if f e r e n t li t h o l o g ie s .
It c o n s is t s
o f w h ite , p in k , an d r e d b lo c k y m u d s t o n e ; w h ite , g r a y , and lig h t g r e e n
h a c k ly , s h a ly , o r n o d u la r lim e s t o n e ; r e d and m a r o o n t h in - and m e d iu m b e d d e d c a lc a r e o u s s i l t sto n e and fin e g r a in e d - s a n d s t o n e , th e la tter l o c a l l y c o n ta in in g s m a ll r e d and b la c k c h e r t p e b b le s .
T h e r e d m u d sto n e
c o m m o n ly -fo r m s b e n c h e s in th e m a p a r e a .
T h e 3 0 -fo o t t h ic k u p p e r u n it c o n s i s t s o f lig h t g r a y t h in - and m ed iu m -,,
b e d d e d g a s t r o p o d - an d o s t r a c o d -b e a r in g f r e s h - w a t e r l i m e s t o n e o v e r la in
b y y e llo w -b r o w n and g r a y s h a ly m u d s to n e .
T h e " g a str o p o d lim e s t o n e "
i s a w id e ly r e c o g n iz e d m a r k e r b e d n e a r o r a t th e to p of th e K o o te n a i in
• s o u th w e s te r n M o n ta n a .
. A c c o r d in g to R o b e r t s (1 9 6 5 , p. B 5 7 ) th e K o o te n a i i s o f E a r ly
C r e t a c e o u s a g e ( la t e A p tia n ).
T h e r m o p o lis S h a le
T h e T h e r m o p o lis S h a le is r e p r e s e n t e d in th e m a p a r e a b y a p p r o x i­
m a t e ly 50 f e e t o f th e lo w e r s a n d s to n e m e m b e r of th e fo r m a t io n .
The
s t r a t a a r e p o o r ly e x p o s e d an d c o n s is t o f a b a s a l y e llo w - b r o w n (I im o n itic )
th in -b e d d e d f in e - a n d v e r y f in e - g r a in e d q u a r tz s a n d s to n e in te r b e d d e d w ith
lig h t and d a r k g r a y v e r y f in e - g r a i n e d s a n d s to n e and s i lt s t o n e .
R o b e rts
(1 9 6 5 ) s t a t e s th a t th e f o r m a t io n l i e s u n c o n fo r m a b ly o n th e K o o te n a i, h is
e v id e n c e b e in g th a t in m a n y p la c e s th e T h e r m o p o lis f i l l s d e p r e s s io n s
in th e la t t e r .
W. A . C ob b an ( o r a l c o m m u n ic a tio n , 1 9 6 3 , in R o b e r t s ,
1 9 6 5 , p. B 5 5 ) b e l i e v e s th e h ia tu s to b e s m a ll, c itin g e v id e n c e th a t th e
44in d e x f o s s i l P r o f e l l i p t i o d o u g la s s i o c c u r s im m e d ia t e ly a b o v e -and b e lo w
th e w id e s p r e a d , d is c o n f o r m it y s e p a r a t in g th e tw o f o r m a t io n s .
I
1■
T h e lo w e r s a n d s to n e m e m b e r is o f E a r l y C r e t a c e o u s a g e , ra n g in g
f r o m l a t e s t A p tia n t o e a r l y A lb ia n ( R o b e r t s , 19 6 5 , p . B 5 7 ).
I m p lic a t io n s o f M a r in e S e d im e n t a r y /S e q u e n c e
T h e m o s t o u tsta n d in g c h a r a c t e r i s t i c of th e P a l e o z o i c and M e s o z o ic
s e d im e n t a r y s e q u e n c e i s it s l e s s e r t h ic k n e s s a s c o m p a r e d to s e d im e n t a r y
s t r a t a o f th e s a m e a g e in ,n e a r b y a r e a s .
In th e m a p a r e a th e t h ic k n e s s
r a n g e s fr o m 2 7 0 0 f e e t to 3 3 0 0 f e e t , w h e r e a s to th e s o u th in th e a d ja c e n t
G a r n e t M o u n ta in q u a d r a n g le , fo r e x a m p le , th e s e q u e n c e i s in e x c e s s of
4 5 0 0 f e e t th ic k .
E a s t of th e m a p a r e a a n e s t im a t e o f th e c o m p a r a b le
s t r a t ig r a p h ic u n its y ie ld s a v a lu e in e x c e s s o f 5 5 0 0 f e e t .
F ro m th e se
d a ta it i s a p p a r e n t th a t th e s t r a t a o f th e m a p a r e a u n d e r w e n t a s o m e w h a t
d if f e r e n t h i s t o r y th a n s t r a t a o f th e b o r d e r in g a r e a s .
T h e m a p a r e a w a s a p p a r e n tly one of s lo w s u b s id e n c e a s c o m p a r e d
to th e b o r d e r in g a r e a s and (m a r in e ) d e p o s it io n m a y l o g i c a l l y b e c o n ­
s id e r e d to h a v e p r o c e e d e d l e s s c o n tin u o u s ly o r at a s lo w e r r a t e .
In ­
d iv id u a l f o r m a t io n s a r e c o m m o n ly th in n e r in th e m a p a r e a th a n in th e
b o u n d in g a r e a s ; f o r m a t io n s th a t a r e th in in th e b o r d e r in g a r e a s m a y b e
a b s e n t in th e -m ap a r e a (fo r e x a m p le , th e b la c k s h a le u n it a t th e b a s e o f
th e L o d g e p o le -and th e P e r m ia n ,P h o s p h o r ia F o r m a t io n ) .
T h is th in n in g
o r a b s e n c e i s in p a r t d u e to th e p e r s i s t e n t p o s it iv e n a tu r e o f th e m a p
a r e a an d th e r e s u lt a n t e r o s io n o f f o r m a t io n s s u b s e q u e n t to t h e ir
45
d e p o s itio n .
It i s a l s o due in p a r t to n o n d e p o s itio n o f s e d im e n t o r
d e p o s it io n a t a r e d u c e d r a t e .
T h is f a c t i s w e l l il lu s t r a t e d e v e n w ith in
th e m a p a r e a b y th e C a m b r ia n R e d L io n F o r m a t io n .
It i s a b ip a r tite
f o r m a t io n th a t i s t h ic k e s t in th e B ig B e a r C r e e k d r a in a g e and c o n s id e r a b ly
th in n e r a to p L a n g o h r N o b .
A t th e la t t e r lo c a t io n b o th th e lo w e r (D ry
C r e e k S h a le ) m e m b e r and th e u p p e r m e m b e r a r e th in n e r th a n a lo n g B ig
B e a r C r e e k an d t h e r e i s n o h ia tu s b e tw e e n th e m e m b e r s .
S lo w e r but
c o n tin u o u s d e p o s it io n i s th u s in d ic a t e d fo r th e L a n g o h r N ob s e c t io n fo r
a t l e a s t th e lo w e r m e m b e r ; th e u p p er m e m b e r m a y h a v e b e e n th in n ed b y
s u b s e q u e n t e r o s io n .
O th er e x a m p le s a r e g iv e n in th e t e x t o f t h is s e c t io n
(S tr a tig r a p h y ) an d f ig u r e 3 g iv e s th e c o m p a r is o n o f f o r m a t io n t h i c k n e s s e s .
4.6
AGE
FORMATION
THICKNESS
(F E E T )
MAP
AREA
CRETACEOUS
>:
THERMOPOLlS SHALE
<
KOOTENAI
UJ
UJ
h
JU R A SSIC
<5
UJ
-J
> 50
GARNET
MOUNTAIN
QUADRANGLE
>400
FM
205
3 6 0 -4 1 2
MORRISON FM
212
2 7 5 -4 5 0
SWIFT FM
58
25-115
RIERDON FM
51
2 8 -6 3
SAWTOOTH
82
120-185
§
2
FM
TR IA S S IC
DlNWOODY FM
O
0 -2 6 5
PERM IAN
PHOSPHORIA FM
O
105-119
PENNSYLVANIAN
QUADRANT QUARTZITE
1 9 8 -3 0 0
1 3 5 -2 5 0
AMSDEN
49 ”78
0 -2 2 5
FM
MISSION CANYON
Ml S S I S S IPPI AN
LODGEPOLE
LIMESTONE
LIMESTONE
BLACK SHALE UNIT
THREE FORKS
FM
375
, 675
440
5 7 5 -6 1 0
3 -5
O
4 0 - 85
1 3 8 -2 2 5
254
3 1 5 -4 5 0
Ul
DEVONIAN
£
JE F F E R S O N
LIMESTONE
_i
UJ
b
<
Tj
FM
RED LION
FM
PILGRIM
PARK
CAMBRIAN
'
MAYWOOD
UJ
-J
Q
Q
LIMESTONE
WOLSEY
7 6 -115
130 - 225,
2 4 5 -2 8 6
1 7 0 -2 5 5 :
40
SHALE
MEAGHER
0 -3 4
O
LIMESTONE
SHALE
"
70
3 0 0 -3 4 0
1 7 5 -2 4 1 ,"
449
-
471
4 0 -1 9 5
1 4 0 -1 7 0
4.0 - 7 5
5 Q - 125
T
?.
5
FLATHEAD
PRECAM BRIAN
QUARTZITE
METAMORPHIC
COMPLEX'
F i g u r e 3. C h a r t c o m p a r in g t h ic k n e s s e s of s e d im e n t a r y u n its in th e
m a p a r e a w ith t h o s e o f th e G a r n e t M o u n ta in q u a d r a n g le .
47
T e r tia r y
E a r l y T e r t i a r y C o n g lo m e r a t e
A c o n g lo m e r a t e s i m i l a r to th e S p h in x C o n g lo m e r a te ( P e a l e ,
1896,
'p. 3) c r o p s out e a s t of th e m o u th of L it t le B e a r C r e e k (SE 1 /4 N E 1 /4 s e c .
3 1 , T . 3S. , R . S E . ), an d i s th e o n ly k n ow n o c c u r r e n c e o f th e u n it in
th e m a p a r e a .
It i s e x p o s e d in a r o a d cu t, f o r m in g an o u tc r o p th a t
m e a s u r e s a p p r o x im a t e ly 6 f e e t h ig h and 150 f e e t lo n g .
T h e c o n g lo m e r a t e
c o n s i s t s of p o o r ly s o r t e d p e b b le s and c o b b le s of P a l e o z o i c c a r b o n a te
r o c k s in a r e d - o r a n g e to w h ite c a l c a r e o u s m a t r ix .
T he p e b b le s and
I
c o b b le s a r e su b a n g u la r to su b ro u n d ed an d h a v e a w h ite h a r d c a lc a r e o u s
c o a tin g ; th e m a t r ix i s e a r t h y , g e n e r a l ly s ilt y , and i s c e m e n t e d b y
p o w d e r y c a l c it e .
R o b in s o n (1 9 6 3 ) in in t e r p r e t in g a s i m i l a r c o n g lo m e r a t e
in th e T h r e e F o r k s q u a d r a n g le d i s c u s s e d tw o p o s s i b l e o r ig in s fo r th e
r e d - o r a n g e c o lo r in th e m a t r ix :
(I ) it m a y r e p r e s e n t a " la t e r it i c s o il
d e v e lo p e d on lo c a l u p la n d s o f lo w r e l i e f d u rin g w a r m and w e t e p is o d e s "
in e a r l y T e r t i a r y t im e ; or (2) th e r e d - o r a n g e c o lo r m a y h a v e b e e n d e ­
v e lo p e d b y g ro u n d w a te r ,' in p a r t b y o x id a tio n of f e r r o u s ir o n fr o m the
c a r b o n a te r o c k s , an d in p a r t b y r e d is t r ib u t io n of f e r r i c ir o n " w a sh ed
f r o m h e m a t it ic p e b b le s d e r iv e d fr o m a v a r i e t y of i r o n - r i c h p r e Q u a te r n a r y r o c k s " .
H e o p p o se d t h is la t t e r v ie w s ta tin g th a t if th e
c o lo r i s p o s t d e p o s it io n a l, th e p e b b le s u r f a c e s sh o u ld b e c o lo r e d r e d o r a n g e a s w e ll a s th e m a t r ix .
T h e s a m e r e a s o n in g can b e u s e d fo r
th e c o n g lo m e r a t e of th e m a p a r e a .
48
T h e f a c t th a t th e c o n g lo m e r a t e i s c o m p r is e d of p o o r ly s o r t e d and
n o t t o o - w e l l r o u n d e d P a l e o z o i c li m e s t o n e d e b r is s u g g e s t s a s o u r c e
th a t w a s n o t fa r d is ta n t.
A t l e a s t fo u r f o r m a t io n s ( P i lg r im , J e f f e r s o n ,
L o d g e p o le , M is s io n C anyon ) a r e r e p r e s e n t e d in th e c l a s t s ; t h is fa c t
c o u p le d w ith th e s i z e an d s o r t in g o f th e c o m p o n e n t r o c k s s u g g e s t s th at
th e s o u r c e a r e a h ad a p p r e c ia b le r e l i e f .
b e p a r t of an a llu v ia l fa n .
T h e d e p o s it , t h e r e f o r e , m a y
S im ila r c o n g lo m e r a t e s c o m p r is e d of c a r b o n a te
c o b b le s h a s b e e n in t e r p r e t e d a s p o s s i b l y b e in g in d ic a t iv e o f e a r l y u p lift
d u rin g th e L a r a m id e o r o g e n y ( L o w e ll and K le p p e r , 1953; R o b in s o n ,
1 963).
T h e a g e o f th e c o n g lo m e r a t e c a n n o t b e d ir e c t ly a s c e r t a i n e d , b u t i n ­
d ir e c t e v id e n c e s u g g e s t s th a t it m a y b e o f e a r l y T e r t i a r y a g e - (P a le o c e n e
or E o c e n e ).
T h e c o n g lo m e r a t e i s b o u n d ed on th r e e s id e s and p a r t ia lly
o v e r la in b y la n d s lid e - m a t e r ia l c o n s is t in g e n t ir e ly of E o c e n e v o lc a n ic
r o c k , y e t th e c o r ig lo m e r a te c o n ta in s n o v o lc a n ic r o c k .
c o n g lo m e r a t e m u s t b e o ld e r th a n th e la n d s lid e d e p o s it .
n o w e x is t ;
T h e r e f o r e , th e
T w o p o s s ib ilitie s
(I ) th e c o n g lo m e r a t e i s y o u n g e r th a n th e v o lc a n ic r o c k (not
th e la n d s lid e ) , o r (2) th e c o n g lo m e r a t e i s o ld e r th a n th e v o lc a n ic r o c k .
T h e la t t e r p o s s i b i l i t y s e e m s to b e th e m o r e r e a s o n a b le d u e to th e
a b s e n c e of v o lc a n ic r o c k in th e c o n g lo m e r a t e -
If p o s s i b i l i t y (I) w e r e
tr u e th e c o n g lo m e r a t e sh o u ld c o n ta in s o m e v o lc a n ic r o c k , a s v o lc a n ic
d e p o s it s m u s t h a v e c a p p e d th e n e a r b y s o u r c e a r e a o f th e la n d s lid e d e b r is .
T h e e v id e n c e s u g g e s t s , t h e r e f o r e , th a t th e c o n g lo m e r a t e i s o f e a r ly
E o c e n e a g e a t t h e y o u n g e s t and m a y p o s s i b l y b e P a l e o c e n e o r e v e n
C r e t a c e o u s in a g e .
49
A ll k n ow n U p p er C r e t a c e o u s and P a l e o c e n e d e p o s it s in a n y
d ir e c t io n fr o m t h is l o c a l i t y , h o w e v e r , a r e c o n g lo m e r a t ic v o lc a n ic
( a n d e s it ic ) s a n d s t o n e s .
T h e d a ta r e g a r d in g c o n g lo m e r a t e s in th e
L iv in g s t o n o f th e B r id g e r - R a n g e s u g g e s t s a s o u r c e s o m e w h e r e to th e
so u th and s o u th w e s t (M c M a n n is,
1 9 6 4 ).
C o n g lo m e r a t e s in th e
" L iv in g s to n " of th e U p p er G a lla tin V a lle y (H a ll,
I 9 6 0 , U npub. P h . D .
T h e s i s , U n iv . of W yo. ) a r e s ig n if ic a n t r e g io n a lly , to o , a s t h e y la c k
P r e c a m b r ia n m e t a m o r p h ic and P a l e o z o i c c o b b le s .
T h e s o u r c e fo r
c o n g lo m e r a t e s e a s t of th e B r id g e r R a n g e , th e n , w a s a p p a r e n tly the
G a lla tin R a n g e - S p a n is h P e a k s - G a lla t in " V a lley " a r e a .
" B a sa l" T e r t i a r y C o n g lo m e r a te
N o t fou n d in th e m a p a r e a i s a " b a sa l" T e r t ia r y c o n g lo m e r a t e r e ­
p o r te d b y M c M a n n is and C h a d w ic k (1 9 6 4 ) a s o v e r ly in g P a l e o z o i c and
P r e c a m b r ia n r o c k s in p a r t s o f th e G a r n e t M o u n ta in q u a d r a n g le and a s
a l s o b e in g p r e s e n t in th e u p p e r M id d le C r e e k d r a in a g e .
T h e u n it is
th in , v e r y p o o r ly e x p o s e d , an d c o n s is t s o f c o b b le s and b o u ld e r s of
P r e c a m b r ia n g n e i s s , a m p h ib o lit e , q u a r tz , and so m e P a l e o z o i c
c a r b o n a te and T e r t i a r y v o lc a n ic r o c k .
T h e c o n g lo m e r a t e m a y b e p r e s e n t
in th e m a p a r e a but w a s n o t fou n d due to th e p o o r e x p o s u r e ; in th e G a r n e t
M o u n ta in q u a d r a n g le it i s e x p o s e d o n ly in r o a d cu ts.
v
r
\
(
50
I
,
\
^
,
E o c e n e S ilt s t o n e
-----------------------------
-
'i
In th e s o u t h e a s t e r n p a r t o f th e m a p a r e a in th e S o u th C o tto n w o o d
C a n y o n d r a in a g e - a r e a a c a r b o n a c e o u s s ilt s t o n e lo c a lly o v e r l i e s
1
' r
,
J u r a s s i c s e d im e n t a r y r o c k s and u n d e r lie s p o s t - l a t e s t e a r l y E o c e n e
v o lc a n ic r o c k s .
:i
T h e c la y s t o n e is g r a y - g r e e n , th in -b e d d e d to f i s s i l e ,
l o c a l l y s ilt y , c a l c a r e o u s , an d c o n ta in s ab u n d an t c a r b o n a c e o u s m a t t e r .
S im ila r d e p o s it s o c c u r in th e M id d le C r e e k d r a in a g e a r e a (W.- M. W e b e r ,
\
U npub. M a s te r o f S c ie n c e T h e s i s , M o n ta n a S ta te U n iv . , B o z e m a n ,
;
an d in th e Squaw C r e e k d r a in a g e a r e a (M cM a n n is and C h a d w ick ,
1965)
1964);
th e la t t e r a u th o r s id e n t if ie d th e c a r b o n a c e o u s m a t e r i a l a s b e in g p la n t
!
I
fr a g m e n ts.
i
S p o r e a n d p o lle n a n a ly s is t e n t a t iv e ly in d ic a te a W a s a tc h ia n
(la t e e a r l y E o c e n e ) a g e fo r th e d e p o s it s in th e Squaw C r e e k a r e a (A . E .
R o b e r t s , w r it t e n c o m m u n ic a tio n ,
1962, in M cM a n n is and C h a d w ick ,
1964, p. 18).
■L a te M io c e n e ? S tr a ta
T e r t i a r y s t r a t a u n d e r ly in g th e e r o s i o n ' s u r f a c e s a lo n g th e G a lla tin
R a n g e fr o n t a r e p o o r ly e x p o s e d b e c a u s e of t h e ir lo w d e g r e e o f in ­
d u r a tio n and b e c a u s e of e x t e n s iv e s u r f i c i a l d e p o s it s of s o i l and g r a v e l.
E x p o s u r e s a r e lim it e d to d r a w s cu t th r o u g h th e s t r a t a b y s t r e a m s ; e v e n
h e r e th e e x p o s u r e s a r e p o o r .
th e m a p a r e a .
N o f o s s i l s w e r e found in t h e s e s tr a ta in
H o w e v e r , H a c k e tt (I 9 6 0 , p. 38) s t a t e s th a t t h e s e b e d s
) -I
a r e e q u iv a le n t to s im il a r s t r a t a in th e C a m p C r e e k H i lls ( n o r th w e s t of
th e m a p a r e a ) , w h ic h h a v e y ie ld e d v e r t e b r a t e f o s s i l r e m a in s d a ted a s
la t e M io c e n e (M . D . M ifflin ,
)
19 6 3 , U npub. M- S. T h e s i s , M on t. S ta te
51
U n iv . , B o z e m a n , p . 15).
S tr a ta t e n t a t iv e ly c o r r e la t e d w ith la t e M io c e n e s t r a t a a r e d e s c r ib e d
f o r t h r e e r e p r e s e n t a t iv e lo c a t io n s in th e m a p a r e a .
L a te M io c e n e ?
s t r a t a c r o p out in th e W 1 /4 s e c . 22 and E 1 /3 s e c . 21, T . 3 S. , R. S E . ,
a t th e m o u th o f S o u th C o tto n w o o d C a n y o n .
T h e lo w e s t e x p o s e d b e d s
c o n s i s t o f w h ite to lig h t g r a y c a lc a r e o u s tu ffa c e o u s fin e - t o m e d iu m g r a in e d q u a r tz s a n d s to n e .
T h e m id d le p a r t of the s e q u e n c e i s c o v e r e d .
T o w a r d th e to p o f th e e x p o s u r e th e s t r a t a c o n s is t of t h in - t o .m e d iu m b e d d e d c a lc a r e o u s t u f f a c e o u s f in e - g r a i n e d s a n d s to n e , th e sa n d g r a in s
a l s o b e in g m u lt ic o lo r e d .
s p a r in g ly .
R e c r y s t a ll iz a t i o n and f r a c t u r e f i l l i n g s o c c u r
T h e t o p m o s t s t r a t a e x p o s e d a r e b u ff to w h ite d e n s e c a lc a r e o u s
a s h , c o n ta in in g a f e w s i l t g r a in s .
C a lc it e f r a c t u r e f i l l i n g s in so m e of
t h is r o c k g iv e s it a " g r a p h ic " a p p e a r a n c e .
A 50 fo o t th ic k s e c t io n o f b a s in s t r a t a c r o p s out in th e SE 1 /4 s e c .
2 9 , T; 3S. , R . S E . ,
on B ig B e a r C r e e k .
T h e s t r a t a c o n s i s t of b u ff
t o b r o w n m e d iu m - to t h ic k - b e d d e d and m a s s i v e g r a y w e a t h e r in g d e n s e
\
li m e s t o n e th at c o m m o n ly e x h ib it s a p itte d s u r f a c e .
W hite c a l c it e
f r a c t u r e f i l l i n g s o c c u r in s t r a t a n e a r th e b a s e of th e -e x p o s u r e .
T h e to p
6 f e e t o f th e u n it d if f e r s o n ly in th a t it c o n ta in s an a b u n d a n ce o f :ajgal
p is o lite s .
A n o th e r o u tc r o p o f la t e M io c e n e ? s t r a t a o c c u r s in t h e - NW 1 /4 s e c .
3 1 , T . 3 S. , R . S E .
It i s b e s t t e r m e d a f a n g lo m e r a t e an d c o n s i s t s of
su b a n g u la r to su b r o u n d e d c o b b le s of g n e i s s , a n d e s it e , and F la th e a d
q u a r tz ite .
T h e in d iv id u a l c o b b le s a r e c o a te d w ith a w e ll c e m e n t e d ch a lk ,
52
b u t a s a u n it th e f a n g lo m e r a te i s v e r y p o o r ly in d u r a te d .
Q u a te r n a r y
A llu v ia l F a n D e p o s it s
A llu v ia l f a n s , p r o b a b ly of la t e P l e i s t o c e n e a g e , a r e d e s c r ib e d
f o r fo u r l o c a l i t i e s in th e m a p a r e a . • A n e x t r e m e ly s m a ll p a r t of a fifth
f a n - - t h e B o z e m a n f a n - - o c c u r s in th e NW 1 /4 s e c .
T . 3 S. , R ., 5 E . , b u t i s n ot d e s c r ib e d h e r e .
14 and N-jr s e c . 15,
In th e
s e c . 3,-
s e c 4 ,, T . 4 S . ,. R . 4 E . , and the. SW 1 /4 s e c . 34,. T . 3 S. , R 4 E , a
fan, e x i s t s th a t i s n o t a c t iv e ly f o r m in g a t p r e s e n t .
T h e s u r f a c e o f th e fan
i s c o v e r e d w ith ab o u t 95% g n e i s s i c m a t e r i a l s and 5% a n d e s it ic la v a
m a te r ia ls .
A n o th e r fa n n o t p r e s e n t ly f o r m in g o c c u r s in th e E -| s e c . 35
an d th e W-| s e c . 36, T . 3 S. , R . 4 E .
T h e lo w e r p a r t of t h is fa n h a s
a b o u t 90% g n e i s s i c m a t e r i a l s and l0% la v a m a t e r i a ls e x p o s e d a t the
s u r f a c e ; th e u p p e r p a r t c o n ta in s a s m a lle r p e r c e n t a g e o f g n e i s s , a
h ig h e r p e r c e n t a g e o f a n d e s it e , but c o n ta in s a p r e d o m in a n c e o f C a m b r ia n
r o c k s , th u s r e f le c t in g it s s o u r c e a r e a w h ic h it a b u tts. pzT w o m o r e fa n s
n o t a c t iv e ly fo r m in g r a d ia t e fr o m Sou th C o tto n w o o d C r e e k an d B ig B e a r
C reek.
C o b b le t y p e s a t th e s u r f a c e s o f t h e s e fa n s w e r e n o t stu d ie d in
d e t a il.
x /l n g e n e r a l th e r o c k s a t th e u p p er r e a c h e s of th e f a n s a r e la r g e r th a n
t h o s e n e a r e r th e b a s e .
R o u n d in g of r o c k s w a s n ot n o ta b ly d if f e r e n t b e t w e e n
th e h e a d an d fo o t fo r e ith e r o f th e s m a lle r f a n s .
L im e s t o n e d e c r e a s e d
p e r c e n t a g e w i s e to w a r d th e fo o t of a ll fa n s an d th e r o c k s p r e s e n t on the
53
fa n s m a p p e d r e f l e c t e d th e l i t h o l o g ie s of s t r a t a n e a r th e h e a d of th e
fa n .
. S tr e a m C h a n n el D e p o s it
A g o o d e x p o s u r e o f a s t r e a m c h a n n e l d e p o s it o c c u r s in a ro a d
cu t in th e SW 1 /4 s e c .
18, T . 3S. , R . 5 E .
T h e d e p o s it c o n s i s t s o f
su b a n g u la r to su b r o u n d e d p e b b le s and c o b b le s , d o m in a te d b y a n d e s it e
(a b o u t 90%) g n e is s (a b o u t 5%) and o th e r r o c k s (about 5%).
Sand, s ilt ,
an d c la y c o m m o n ly f i l l th e v o id s b e tw e e n th e la r g e r f r a g m e n t s or
c la .s ts .
T h e g n e i s s i s d e e p ly w e a t h e r e d , s u g g e s t in g th a t th e d e p o s it
m a y b e o f m id d le ? P l e i s t o c e n e a g e .
IG N E O U S'R O C K S
T e r t i a r y V o lc a n ic R o c k s
V o lc a n ic r o c k s in th e m a p a r e a u p c o n fo r m a b ly o v e r l ie P r e c a m b r ia n m e t a m o r p h ic r o c k s , P a l e o z o ic , M e s o z o ic , and s o m e e a r ly
T e r t i a r y s e d im e n t a r y r o c k s .
T h e m a x im u m t h ic k n e s s of th e v o lc a n ic
s e q u e n c e iq th e m a p a r e a i s ab ou t 1400 f e e t ; M cM a n n is find C h a d w ick
(1 9 6 4 , p . 19) n o te th a t in th e a d ja c e n t G a r n e t M o u n ta in q u a d r a n g le a
t o t a l t h ic k n e s s in e x c e s s o f 4 0 0 0 f e e t a p p a r e n tly e x i s t e d a t one t im e .
T h e s e q u e n c e d ip s g e n t le to th e n o r th in th e m a p a r e a .
T w o v o lc a n ic t y p e s a r e d o m in a n t in th e m a p a r e a , 9-s in th e G a r n e t
M o u n ta in q u a d r a n g le .
(I ) T h e f i r s t ty p e c o n s i s t s of la v a f lo w s o f
b a s i c a n d e s it e in t e r s t r a t if ie d w ith flo w b r e c c i a s .
T h e d o m in a n t r o c k
ty p e i s a ta n w e a t h e r in g d a r k g r a y to b la c k d e n s e b a s i c a n d e s it e th at
i s c o m m o n ly s lig h t ly p o r p h y r it ic .
T h e la v a s e q u e n c e o c c u r s a s a
s e r i e s o f in d iv id u a l f lo w s s u p e r im p o s e d u p on on e a n o th e r .
m a t e r i a l c a n b e d iv id e d in to tw o m a in ty p e s :
The
(a) m a s s i v e c r y s t a llin e
c o lu m n a r - j o in t e d r o c k , an d (b) flo w b r e c c i a c o m p r is e d o f a n d e s ite
r o c k s s e t in a v a r i c o lo r e d m a t r ix c o n s is t in g o f (a c c o r d in g to M cM a n n is
and C h a d w ic k , 1964) " fin e ly g ro u n d li t h i c f r a g m e n t s and la b r a d o r it e
and p y r o x e n e c r y s t a l s , "
(2)
T h e s e c o n d d o m in a n t v o lc a n ic ty p e i s l e s s c o p im o n th an th e
f i t s t and c o n s i s t s o f c r u d e ly s t r a t if ie d b r e c c i a c o n ta in in g s e v e r a l
v o lc a n ic l i t h o l o g i e s , b u t m a in ly b a s ic a n d e s it e .
T he c o m p o n e n t r o c k s
r a n g e fr o m fr a g m e n t a l to b o u ld e r s i z e and v a r y fr o m s u b r o u n d e d to
55
a n g u la r .
T h e m a t r ix o f th e b r e c c ia c o n ta in s s m a ll l i t h i c f r a g m e n t s .
B o th v o lc a n ic t y p e s (I and 2) a r e d e s c r ib e d in g r e a t e r d e t a il b y
M c M a n n is and C h a d w ick (1 9 6 4 , p. 1 9 - 2 3 ) , in c lu d in g c h e m ic a l a n a ly s e s .
T h e a g e o f th e v o lc a n ic s e q u e n c e i s b a s e d in p a r t on th e d a tin g of
s p o r e s in th e u n d e r ly in g la t e e a r l y E o c e n e s i l t sto n e (M c M a n n is and
C h a d w ic k ,
1 9 6 4 ).
A r e c e n t p o t a s s iu m - a r g o n d a te o b ta in e d fr o m a
s a m p le ta k e n 700 to 8 0 0 f e e t a b o v e th e b a s e of th e v o lc a n ic s e q u e n c e
on th e E a s t F o r k o f M id d le C r e e k ( s o u t h e a s t o f th e m a p a r e a ) y ie ld e d
a n a g e o f 4 2 . 7 ( - 2. 4) m . y . - - late: E o c e n e (W. J. M c M a n n is , p e r s o n a l
c o m m u n ic a tio n ,
1966).
H a ll (1 9 6 0 , U npub. P h . D . T h e s i s , U n iv . of
W yo. ) h a s s u g g e s t e d th a t s o m e o f th e G a lla tin R a n g e v o l c a n i c s rd ay
b e a s y o u n g a s O lig o c e n e .
I n tr u s iv e R o c k s
Ig n e o u s in t r u s iv e b o d ie s o c c u r in th e s o u th w e s t c o r n e r o f th e m a p
a r e a (in s e c . 2,
10, an d 11, T . 4 'S. , R . 4 E . ) w h e r e th e y cu t P r e -
c a m b r ia n m e t a m o r p h ic r o c k .
T h e i n t r u s i v e s a r e id e n t ic a l to th e
S h e n a n g o C r e e k in t r u s iv e m a s s of M c M a n n is and C h a d w ick (1 9 6 4 ,
p. 2 8 ), b e in g a lig h t g r a y da c ite p o r p h y r y w ith p h e n o c r y s t s o f
o l i g o c l a s e , b io t it e , and s o m e h o r n b le n d e .
T h e c l o s e n e s s of th e tw o
in t r u s iv e a r e a s (a b ou t one m il e a p a r t) an d th e id e n t ic a l lit h o lo g y of
th e in t r u s iv e b o d ie s s u g g e s t th a t a ll a r e p a r t o f th e s a m e m a s s .
T h e a g e o f th e S h en a n g o in t r u s iv e m a s s is not d ir e c t ly known;
h o w e v e r , a c c o r d in g to t h e .f o llo w in g l i n e s o f e v id e n c e , it i s b e lie v e d
to b e T e r t i a r y .
F o u r l i t h o l o g ic a l ly s im il a r in t r u s iv e b o d ie s (in c lu d in g
5.6
th e S h e n a n g o in t r u s iv e ) o c c u r -in th e G a r n e t M ou n tain q u a d r a n g le ,
t h r e e of w h ic h t r a n s e c t th e T e r t i a r y v o lc a n ic s e q u e n c e and a r e th u s
y o u n g e r th a n th e v o lc a n ic r o c k s .
T he f o u r t h - - t h e S h e n a n g o C r e e k
in t r u s iv e m a s s - - d o e s n o t t r a n s e c t v o lc a n ic r o c k s , b u t, lik e th e oth er
th r e e in t r u s iv e b o d ie s , i s lo c a t e d a lo n g a m a jo r fa u lt w h ic h a p p a r e n tly
a c te d a s a co n d u it fo r th e in t r u s iv e m a t e r i a l.
The age of m o v em en t
on th e S quav/ C r e e k fa u lt, a lo n g w h ic h th e S h en a n g o in t r u s iv e i s
lo c a te d , c o u ld b e a n y t i m e b e tw e e n L a te C r e t a c e o u s and e a r l y E o c e n e .
T h e r e f o r e , a t.t h e o ld e s t th e S h en a n g o in t r u s iv e i s L a te C r e t a c e o u s ,
b u t s i m i l a r i t y to o th e r i n t r u s i v e s s u g g e s t s a T e r t ia r y a g e (M cM a n n is
an d C h a d w ic k , 1 9 6 4 ).
A p o t a s s iu m - a r g o n a n a ly s is o f a s i m i l a r d a c it ic
in t r u s iv e n e a r M ill C r e e k (a p p r o x im a t e ly 35 m i l e s e a s t - s o u t h e a s t o f
th e S h e n a n g o C r e e k in t r u s iv e a r e a ) y ie ld e d an a g e of 4 9 . O -
1 .7 m . y. -
m id d le . E o c e n e ( p e r s o n a l c o m m u n ic a tio n , W., J . M c M a n n is,
1966).
A lth o u g h th e M ill C r e e k in t r u s iv e i s q u ite f a r d is ta n t, it i s p o s s ib ly
d e v e lo p e d a lo n g th e s a m e s t r u c t u r a l w e a k n e s s a s th e S h e n a n g o C r e e k
in t r u s iv e .
STR U C TU R E
G eneral
T h e G a lla tin R a n g e l i e s w ith in the' s o u t h e a s t e r n e x t r e m i t y o f th e
N o r th e r n R o c k y M o u n ta in P r o v in c e o f F e n n e m a n (1 9 3 1 ).
S t r u c t u r a lly ,
h o w e v e r , it i s u n lik e th e m o u n ta in s o f t h i s p r o v in c e a,nd sh o u ld h e c o n ­
s id e r e d a p a r t of th e C e n tr a l R o c k y M o u n ta in P r o v in c e , b e c a u s e "the
r a n g e s of th e N o r th e r n R o c k y M ou n ta in ? a r e f o r m e d fr o m lo n g , n a r r o w ,
c l o s e l y s p a c e d f o ld s an d t h r u s t b lo c k s m a d e up of g e o s y n c li n a l s e d i ­
m e n t a r y r o c k s a lo n e , n o t of b a s e m e n t r o c k s " (K ing,
1959, p.
137).
The
C e n tr a l R o c k y M o u n ta in s a r e b r o a d - b a c k e d u p lif t s , c o m m o n ly w ith w id e
a r e a s o f b a s e m e n t r o c k e x p o s e d in t h e ir c o r e s ; a ls o , th e y a r e o f d iv e r s e
t r e n d an d w id e ly s p a c e d , w ith b r o a d e r b a s in a r e a s in b e t w e e n (K in g, 195 9,
p. 112).
T h e s t r u c t u r e o f th e G a lla tin an d a d ja c e n t a r e a s b e t t e r f it s th e
la t t e r d e s c r ip t io n .
The m a p a r e a l i e s w ith in th e n o r t h e r n p a r t o f th e G a lla t in R a n g e and
c o n s t it u t e s a p a r t o f w h a t g l o s s (1 9 5 0 ) c a l l s th e W y o m in g S h e lf,
The
s e d im e n t a r y c o v e r of th e s h e lf i s g e n e r a l ly th in ( l e s s th a n 3 3 0 0 f e e t th ic k
in th e m a p a r e a ) - - t o o th in to h a v e .e x e r t e d m u c h c o n t r o l o v e r the s t r u c t u r e s
fo r m e d b y th e g e n e r a l e a s t - n o r t h e a s t K a r a m id e c o m p r e s s i v e s t r e s s .
The
s h e lf d e p o s it s a r e o f r e l a t i v e l y u n ifo r m t h in n e s s w h e r e a s d e p o s it s of a
g e o s y n c lin e a r e t h ic k c e n t r a l ly and th in s h e lfw a r d .
D u r in g c o m p r e s s io n
s t r a t a o f th e t h ic k p n rt of th e g e o s y n c lin e m o v e s h e lfw a r d and a r e b r o k e n
a lo n g a s e r i e s of t h r u s t f a u lt s ; th e r e a s o n i s th a t the b a s e m e n t r o c k u n d e r ­
ly in g th e g e o s y n c lin e i s n e a r e r th e s u r f a c e s h e lfw a r d an d th e s t r a t a a r e
58
f o r c e d to r i s e o v e r th e b u t t r e s s , r u p tu r in g in th e p r o c e s s .
It is
c o m m o n ly b e li e v e d th a t th e r e s u lt in g s t r u c t u r e s o f th e s h e lf r e g io n
a r e e x p r e s s i o n s o f a n c ie n t t r e n d s in th e P r e c a m b r ia n b a s e m e n t , r e ­
a c t iv a t e d d u r in g th e L a r a m id e o r o g e n y .
T h e h is t o r y of s o m e of th e
f a u lt s a s r e c o r d e d in th e s e d im e n t a r y s e q u e n c e ( t h ic k n e s s a n d f a c i e s
d is tr ib u tio n ) i s th e b a s i s fo r im p ly in g th a t s o m e h a v e d e f in it e ly had
a lo n g h i s t o r y of m o v e m e n t s d a tin g fr o m P r e c a m b r ia n t im e . O ther
i
f a u lt s o f s i m i l a r t r e n d a re,, b y a n a lo g y , b e li e v e d to b e of s im ila r
v in ta g e .
T h e d o m in a n t s t r u c t u r e s g e n e r a l ly tr e n d w e s t - n o r t h w e s t , ■
w h e r e a s l e s s o b v io u s s t r u c t u r e s tr e n d n o r t h e a s t ( s e e f ig u r e 4 ).
R e g io n a l T e c t o n ic P a t t e r n
I n te r p r e ta t io n o f s t r u c t u r e s in th e m a p a r e a r e q u ir e s ,a k n o w le d g e
o f r e g io n a lly s a lie n t s t r u c t u r e s an d o f th e g rcjss c a u s a l m e c h a n is m .
In s o u t h - c e n t r a l and s o u th w e s t M on tan a i s a g r o u p o f p r o m in e n t s t r u c t u r e s ,
th e m e m b e r s o f w h ic h a r e o r ie n te d w e s t - n o r t h w e s t .
T w o o f th e m d e ­
s e r v in g of d i s c u s s i o n h e r e a r e th e L a k e B a s in fa u lt zo n e an d th e N y e B o w le r lin e m e n t .
T h e L a k e B a s in fa u lt zo n e i s in e x c e s s o f 100 m i l e s lo n g and c o n s i s t s
o f a s e r i e s of en e c h e lo n n o r t h e a s t s t r ik in g n o r m a l f a u lt s th a t fo r m a
m a jo r w e s t - n o r t h w e s t tr e n d in g z o n e . - S t r a t ig r a p h ic e v id e n c e a c r o s s th e
fa u lt in d ic a t e s p e r io d ic m o v e m e n t th a t in flu e n c e d s e d im e n t a t io n , p a r t i ­
c u la r ly d u r in g p o s t - M a d is o n , p r e - J u r a s s i c t im e .
T h e B ig S n o w y G roup
i s p r e s e n t n o r th of th e fa u lt and i s a b s e n t on th e sou th ; th e Q u ad ran t and
C h u g w a te r a r e p r e s e n t m a in ly to th e so u th of th e fa u lt z o n e b u t a r e a b s e n t
59
Crozy Mtn.
Intrusive Complex
Monzonite
lnt.
■ Wi Isall
CRAZY
•T h re e Forks
MOUNTAI NS
GALLATI N
BASI N
VAL L EY
BOZEMAN
LIVINGSTON
Upper
Squow Cr.
lnt.
Lone Mtn.
lnt. X
Emigrant - Mill Cr.
Rarcupine Cr.
X lnt.
Intrusive
Complex
Jordine
lnt. Complex
Upper
Gallatin
G ardiner
_ Montono _
Wyoming
T-Electric Pk.
LEG EN D
Thrust or Reverse Fault
--'T'''
Anticline
Inferred
^
Syncline
Overturned
Fault
—
Overturned
Strike Slip Fault
Igneous
Intrusive
__ M a p Area
5
IO
Anticline
Syncline
Boundary
15 Miles
Y e llo w s to n e »
F ig u r e 4. M ap s h o w in g m a j o r s t r u c t u r a l f e a t u r e s of th e r e g io n n e a r th e
m ap a rea .
60
t o th e n o r th (A lp h a and F a n s h a w e 1 1 9 5 4 ).
D u r in g th e L a r a m id e
o r o g e n y , th e e a s t - n o r t h e a s t compares.s'ive s t r e s s w a s r e s o lv e d in to
a l e f t - l a t e r a l s t r i k e - s l i p r p o v e m e n t a lo n g t h is p r e - e x i s t i n g zo n e of
w e a k n e s s (B a d g le y ,
19 6 5 , p. 109).
T h e L a k e B a s in fa u lt z o n e i s
b e li e v e d b y s o m e w o r k e r s to tie a c o n tin u a tio n of th e O sb o r n fa u lt
zo n e (M on tan a lin e a m e n t ) , a w e s t - n o r t h w e s t o r ie n te d f e a t u r e t r a n ­
s e c t in g w e s t e r n M o n ta n a .
F o r c r i t i c a l o b s e r v a t io n s on th e s u b je c t
th e r e a d e r i s r e f e r r e d to B la c k ^ to n e (1 9 5 6 ), W a lla c e ap d o t h e r s
(1 9 6 0 ), G w fnn ( 1 9 6 1 ) ,. K a u ffm a n (1 9 6 3 ), a n d Sm Ith (1 9 6 5 ).
T h e N y e - B o w le r lin e a m e n t i s a p p r o x im a t e ly 115 m i l e s lo n g and
c o n s i s t s of a s e r i e s of a n t ic l in e s , f a u lt s , d o m e s , v o lc a n ic f e a t u r e s ,
an d l a c c o l i t h s .
It t r e n d s p a r a lle l, to th e L a k e B a s in fa u lt z o n e and,
lik e ttie l a t t e r , e x h ib it s e v id e n c e o f l e f t - l a t e r a l s t r ik e - s lip m o v e ­
m e n t (A lp h a an d F a ,n sh a w e ,
1 954).
In r e la t io n to th e B e a r t o o t h M o u n ta in s
th e lin e a m e n t m a y ( I ) t e r m in a t e a g a in s t th e n o r t h w e s t t r e n d in g fr o n ta l
e d g e of th e m o u n ta in s , ( 2 ) e x te n d n o r t h w e s t p a r a ll e l to and m e r g e w ith
th e m a r g in of th e B e a r t p o t h m a s s i f , o r (3) t r e n d w e s t w a r d a lo n g th e
M ill P r e e k - - S t i l l w a t e r s t r u c t u r a l z o n e , th u s d iv id in g ‘th e n o r th w e s t
p a r t of th e B e a r t o o t h M o u n ta in s in to s e p a r a t e s t r u c t u r a l b lo c k s
( F o o s e and o t h e r s ,
1961).
T e c t o n ic P a t t e r n s o f A d ja c e n t A r e a s
T h e ty p o g r a p h ic e x p r e s s i o n o f th e L a r a m id p o r o g e n y in th e im m e d ia te
r e g io n c o n s i s t s o f fa u lt b lo c k m o u n ta in s and in t e r m o n ta n e b a s in s .
M a jo r
61
g e o g r a p h ic
2
u n it s in th e im m e d ia te v ic in it y of th e G a lla tin R a n g e i n ­
c lu d e th e S p a n ish P e a k s , th e B e a r t o o t h M o u n ta in s, th e M a d iso n and
B r id g e r r a n g e s , and th e T h r e e F o r k s and C r a z y M o u n ta in s b a s in s .
T h e G a lla tin , M a d is o n , S p a n ish P e a k s , an d B e a r t o o t h a r e a s , and th e
s o u th e r n p a r t o f th e B r id g e r R a n g e a r e t y p if ie d b y th e fo llo w in g
c h a r a c te r is tic s :
(I ) h ig h - a n g le r e v e r s e and n o r m a l f a u l t s ,. ( 2.)
a b s e n c e of B e lt s t r a t a , (3) e x t e n s iv e e x p o s u r e s o f p r e - B e l t m e t a '
'
<
I
_
m o r p h ic r o c k , and (4) t h in n e s s o f th e P a l e o z o i c and M e s o z o ic s t r a t a
' (M c M a n n is , 1'965).
T h e 'S p a n is h P e a k s b o r d e r p a r t o f th e G a lla tin R a n g e on th e w e s t
an d a r e g e o g r a p h ic a lly s e p a r a t e d fr o m th e la t t e r b y th e G a lla tin
R iv e r ; s t r u c t u r a lly , h o w e v e r , th e S p a n ish P e a k s a r e e q u iv a le n t to the
c e n t r a l p a r t o f th e G a lla t in R a n g e .
On th e n o r t h e a s t th e S p a n is h P e a k s
a r e d e lim it e d b y th e n o r t h w e s t tr e n d in g S q uaw C r e e k - - C h e r r y C r e e k
f a u l t - - a n o r t h e a s t d ip p in g r e v e r s e fa u lt a lo n g m o s t o f i t s le n g th ;
On
th e s o u th w e s t s id e th e S p a n is h P e a k s a r e b o u n d ed b y a n o th e r n o r th w e s t
tr e n d in g , n o r t h e a s t d ip p in g r e v e r s e fa u lt, b e li e v e d b y S w a n so n (1 9 5 0 )
to b e a c o n tin u a tio n of th e G a r d in e r r e v e r s e fa h lt.
F a r t h e r so u th th e G a lla t in .R iv e r s e r v e s to s e p a r a t e th e s o u th e r n
p a r t of th e G a lla tin R a n g e on th e e a s t f r o m th e n o r th e r n b lo c k of th e
G e o g r a p h ic u n its a r e u s e d h e r e b e c a u s e th e f e a t u r e s (m o u n ta in s
an d b a s in s ) o f th e a r e a h a v e b e e n d e lin e a t e d on a to p o g r a p h ic b a s is
o n ly , an d th u s a r e n o t n e c e s s a r i l y s t r u c t u r a l u n its .
62
M a d is o n R a n g e on th e w e s t .
T h e d o m in a n t s t r u c t u r e in t h is b lo c k of th e M a d iso n R a n g e i s th a t
o f a " b road , f la t s y n c lin e tr e n d in g w e s t o f n o r th and h a v in g a s h a r p ly
f o ld e d and fa u lte d w e s t e r n fla n k " (S w a n so n ,
1950, p. 7).
T h e la t t e r
fo ld in g and r e la t e d fa u ltin g c a u s e d S w a n so n to p r o p o s e tw o s t r e s s
d ir e c t io n s w ith c o m p r e s s io n o c c u r r in g f i r s t fr o m th e w e s t , la t e r
fr o m th e n o r t h e a s t , an d s u b s e q u e n tly fr o m th e w e s t a g a in .
An ea st-
n o r t h e a s t c o m p r e s s iv e s t r e s s i s a ll th a t n e e d b e r e q u ir e d if it is
r e m e m b e r e d th a t (I ) th e b a s e m e n t r o c k s a r e n ot h o m o g e n e o u s , and
d e v ia tio n o f s t r u c t u r a l t r e n d s e x p e c t e d t o r e s u lt fr o m th e n o r t h e a s t
c o m p r e s s i v e s t r e s s a r e to b e a n t ic ip a t e d , and th a t ( 2) y ie ld t o s t r e s s .
sh o u ld h ot b e s im u lt a n e o u s .e v e r y w h e r e .
T h e n o r th w e s t tr e n d in g B e a r t o o t h M o u n ta in s li e s o u t h e a s t o f th e
G a lla tin R a n g e and a r e s e p a r a t e d fr o m th e la t t e r b y a h ig h - a n g le ,
n o r t h e a s t tr e n d in g fa u lt (th e Y e llo w s t o n e V a lle y fa u lt). . D ip - s l ip
m o v e m e n t on t h is fa u lt p r o b a b ly d e v e lo p e d a s a c o m p le m e n t to r e v e r s e
fa u ltin g a lo n g th e n o r t h e a s t s id e of th e B e a r t o o t h M o u n ta in s. . M cM a n n is
(1 9 6 4 , p . 4)
h a s fou n d e v id e n c e to s u g g e s t th a t th e Y e llo w s t o n e V a lle y
fa u lt h ad a lr e a d y b e e n a c t iv e p r e v io u s to L a r a m id e d e fo r m a tio n .
e v id e n c e is :
The
(I) lo w - a n g le fo ld e d t h r u s t s and lin e a r f o ld s t y p if y the
a r e a w e s t of th e Y e llo w s t o n e , w h e r e a s e a s t of the v a ll e y , f a u lt s a r e
s t e e p an d f o ld s a r e not a s co m m o n ; and ( 2) th e r e i s a la r g e i n c r e a s e in
t h ic k n e s s o f B a te C r e t a c e o u s (and a p p a r e n tly P a le o c e n e ) . s t r a t a fr o m
e a s t to w e s t a c r o s s a n o r th w a r d p r o j e c t io n o f the Y e llo w s t o p e V a lle y
63
fa u lt tr e n d , an d c o r r e s p o n d in g d e e p e n in g i s e v id e n t in th e C razyM o u n ta in s b a s in .
T he B r id g e r R a n g e i s a n o r t h - s o u t h o r ie n te d u p lift ly in g n o rth
o f th e G a lla tin R a n g e .
It a p p e a r s to b e th e la r g e e a s t lim b of a
s t r u c t u r a lly c o m p le x , n o r t h e a s t p lu n g in g -a n tic lin e w h ic h h a s b e e n
s e v e r e d fr o m th e w e s t e r n lim b b y p o s t - l a t e P a le o c e n e n o r m a l
fa u ltin g . . T h e r a n g e i s d iv id e d in to n o r t h e r n an d s o u th e r n p a r ts b y
th e R o s s P a s s fa u lt z o n e . . S ou th o f th e fa u lt zo n e no B e l t s t r a t a a r e
p r e s e n t w h e r e a s to th e n o r th a th ic k B e l t s e q u e n c e i s p r e s e n t ; t h is
fa u lt zo n e w a s a c t iv e in P r e c a m b r ia n t im e ,(M c M a n n is, 1955; 1963).
T h e T h r e e F o r k s b a s in b o u n d s th e n o r t h w e s t s id e o f th e G a lla tin
R a n g e an d i s s e p a r a t e d fr om -the -latter b y a h ig h - a n g le n o r m a l fa u lt.
(F u r th e r in t e r p r e t a t io n of th e s o u th e r n p a r t of th e b a s in w i l l b e m a d e
la t e r . ) T r e n d in g e a s t - w e s t a c r o s s th e n o r th e r n end of th e b a s in i s a
m o n o c lin a l fo ld b e li e v e d b y H a c k e tt a n d o t h e r s ( i9 6 0 ) to r e f l e c t a
s u b s u r fa c e f a u l t - - t e r m e d th e C e n tr a l P a r k fa u lt.
It c o in c id e s
a p p r o x im a t e ly w ith th e w e s t w a r d e x t e n s io n of th e . R o s s P a s s fa u lt
z o n e , and lik e th e la t t e r , a p p a r e n tly c o in c id e d a p p r o x im a t e ly w ith th e
s h o r e lin e o f th e B e lt se a . (L a te P r e c a m b r ia p ) .
. T h e C r a z y M o u n ta in 's b a s in l i e s n o r t h e a s t of th e m a p a r e a and is
a s t r u c t u r a lly c o m p le x d o w n w a rp ed ; a r e a w h o s e d e f o r m a t io n i s i n ­
t im a t e l y r e la t e d to th a t of th e G a lla tin R a n g e . . T h e e a s t e r n m a r g in of
th e b a s in i s cu t b y th e n o r t h e a s t tr e n d in g C r a z y M o u n ta in 's d is tu r b e d
zo n e ^a n o r th e a s t w a r d e x t e n s io n of th e Y e llo w s t o n e V a lle y fa u lt z o n e),
64
(a s p r e v io u s ly d e s c r ib e d ) to th e w e s t o f w h ic h s t r u c t u r a l c o n to u r s
s u g g e s t an a b ru p t in c r e a s e in t h ic k n e s s of U p p er C r e t a c e o u s and
P a l e o c e n e s tr a ta ; r a p id th ic k e n in g of th e s a m e s t r a t a i s in d ic a te d
to th e e a s t of th e B a t t le R id g e m o n o c l i n e , . a s t r u c t u r a l f e a t u r e of
th e w e s t - c e n t r a l p a r t of th e b a s in w h ic h e x h ib it s d ip s th a t a r e
v e r t i c a l to o v e r tu r n e d a lo n g it s le n g th (D o b b in and E r d m an il, 1955).
S e i s m i c d a ta in d ic a t e th e m o n o c lin e i s d e v e lo p e d a lo n g a s u b s u r f a c e
V
f a u lt , an d th a t a th ic k p r e - F la t h e a d s e d im e n t a r y s e q u e n c e l i e s on
th e n o r th w e s t s id e ( p e r s o n a l c o m m u n ic a t io n ,. W. J. M cM anh is,,
1966).
D u r in g th e L a r a m id e o r o g e n y th e C r a z y M o u n ta in 's B a s in d is tu r b e d
z o n e - - Y e llo w s t o n e V a lle y fa u lt tr e n d s e r v e d .a s an e a s t e r n b o u n d a ry ,
an d th e B a ttle R id g e s u b s u r f a c e f a u l t - - s o u th e r n "end" o f t h e .B r id g e r
R a n g e tr e n d s e r v e d a s th e w e s t e r n b o u n d a r y o f a s t r u c t u r a l lo w .
In ­
c r e a s i n g c o m p r e s s io n " ch a n n eled " th e s e d im e n t a r y s e q u e n c e of th e
C r a z y M o u n ta in 's B a s in s o u th w e s tw a r d o n to th e s t r u c t u r a lly lo w ly in g n o r th -e n d o f th e G a lla tin :R a n g e .
T h e s t r u c t u r e s p r o d u c e d c o n s is t,
o f a r c u a t e , en e c h e lo n a n t ic lin e s and n o r t h e a s t d ip p in g r e v e r s e fa u lts
th a t a r e c o n v e x to th e s o u th w e s t (S k e e l s ,
1 9 3 9 ). - A t th e s a m e t im e t h e s e
s t r u c t u r e s w e r e d e v e lo p in g , the- B r id g e r u p lift w a s b e in g f o r c e d e a s t ­
w a r d and th e B e a r t o o t h u p lift n o r t h e a s t w a r d ( R o b e r ts ,
1 9 6 5 ).
The T h ree
F o r k s B a s in d id n o t e x i s t d u r in g th e t i m e o f d e fo r m a tio n , b u t w a s a
m o u n ta in o u s a r e a w h ic h a c t e d a s a r e s i s t a n t s t r u c t u r e .
F r o m th e f o r e g o in g d i s c u s s i o n tw o m a j o r c o n c l u s io n s ■a r e w a r r a n te d :
(I ) a l l m a jo r s t r u c t u r e s (o r L a r a m id e r e a c t iv a t io n t h e r e o f ) ca n be
65
e x p la in e d b y an e a s t - n o r t h e a s t c o m p r e s s iv e s t r e s s ; and (2 ) t h e r e is
a m p le e v id e n c e to in d ic a t e th a t m a jo r s t r u c t u r a l w e a k n e s s e s e x is t e d
p r io r to th e L a r a m id e o r o g e n y and w e r e r e a c t iv a t e d d u r in g th e
o r o g e n y . - S i m i l a r ' s t r u c t u r e s and t r e n d s sh o u ld e x i s t w ith in th e m a p
area.
S o u th 'C o tto n w o o d C r e e k F a u lt
T h e g r o s s e a s t - n o r t h e a s t c o m p r e s s iv e s t r e s s c a u s e d r e v e r s e
fa u ltin g a lo n g
a fa u lt lo c a t e d in th e S ou th C o tto n w o o d C r e e k d r a in a g e ,
h e r e n a m e d th e S o u th C o tto n w o o d C r e e k fa u lt. , S im u lt a n e o u s ly , a n d /o r
p o s s i b l y s ta r tin g s o m e w h a t la t e r , f a u lt s d e v e lo p e d a p p r o x im a t e ly p e r ­
p e n d ic u la r to th e Sou th C o tto n w o o d C r e e k fa u lt and m o s t l i k e l y ow e
t h e ir e x i s t e n c e to d if f e r e n t ia l m o v e m e n t o f th e b lo c k s w h ic h th e y
b order.
T h e South' C o tto n w o o d C r e e k fa u lt i s th e m a jo r n o r t h w e s t tr e n d in g
fa u lt in th e m a p a r e a .
A s w a s o r ig in a lly s u g g e s t e d b y P e a l e (1 8 9 6 , p. 3),
it a p p e a r s to b e a c o n tin u a tio n o f th e S a l e s v i l l e fa u lt ( s e e f ig u r e 4)
p r e s e n t to th e n o r t h w e s t o f th e -m a p a r e a , b u t in t e r v e n in g v a l l e y d e p o s it s
m a s k a n y c o n n e c tio n o f th e tw o .
A ls o , p o s s i b l e h o r iz o n t a l d is p la c e m e n t
on th e G a lla tin R a n g e fr o n t fa u lt h a s o f f s e t a n y su ch c o n n e c tio n .
T h e South' C o tto n w o o d C r e e k fa u lt d ip s s t e e p ly to th e n o r t h e a s t a lo n g
m o s t of i t s le n g th and e x h ib it s a r e v e r s e r e la t io n s h ip .
In s e c . 36 ,. T.
3 S. , R . 5- E . , t h is r e v e r s e fa u lt i s t r a n s e c t e d b y a c r o s s fa u lt (the
W h e e le r G u lc h fa u lt, d e s c r ib e d la t e r ) .
N o r th w e s t o f th e c r o s s fa u lt,
7000
-
J sa- Jr - Jsw- Jm
6500 -
6000
5500 -
5000 -
4500 -
4000 -
7500
7000 -
- -
Jsa - Jr -Jsw-Jm
6500
6000
-
5500 -
5000
4500 -
4 0 0 0 J----------------------------------------------------------------------------------------------------------------------- ------------------------- --------- *---------
F ig u r e 5. E n la r g e d s p e c u la t iv e c r o s s - s e c t i o n s of s t r u c t u r e s a lo n g e a s t ­
tr e n d in g e x t e n s io n of th e South C o tto n w o o d C r e e k fa u lt (N^ s e c . 6 ,
R. 6 E . }
R. 6 E
67
m in im u m s t r a t ig r a p h ic d is p la c e m e n t on th e r e v e r s e fa u lt i s in e x c e s s
of 4 0 0 0 fe e t; P r e c a m b r ia n m etam orp h icp r o c k on th e u p th ro w n (n o r th e a s t) •
s id e l i e s a g a in s t a ll s t r a t ig r a p h ic u n its f r o m C a m b r ia n to P e n n s y lv a n ia n
o f th e d o w n d r op p ed .sid e .
S o u th e a s t o f th e c r o s s fa u lt, m in im u m s t r a t i ­
g r a p h ic d is p la c e m e n t on th e r e v e r s e fa u lt i s a p p r o x im a t e ly 1600 fe e t;
C a m b r ia n to M i s s i s s i p p i a n s t r a t a of th e u p th ro w n s id e l i e a g a in s t
C r e t a c e o u s s t r a t a o f th e d ow n d r op p ed s id e .
In th e N E 1 /4 s e c .
I, T . 4' S.
R. B E . ,
fa u lt i s c o n c e a le d b y v o lc a n ic r o c k .
th e Sou th C o tto n w o o d C r e e k
T w o o th e r fa u lts m e e t a t a p p r o x i­
m a t e ly th e s a m e lo c a tio n , on e o f w h ic h t r e n d s e a s t fr o m th e ju n c tio n and
th e o th e r o f w h ic h t r e n d s s o u th w e s t.
T h e a c t u a l ju n c tio n o f th e fa u lts is
c o n c e a le d b y th e v o lc a n ic c o v e r ; c o n s e q u e n tly , th e q u e s tio n a r i s e s a s
to w h at h a p p e n s to th e S ou th C o tto n w o o d C r e e k fa u lt?
T h e p o s s i b i lit y
e x i s t s th a t it m a y e x te n d b e n e a th th e v o lc a n ic c o v e r and r e t a in it s
n o r th w e s t s t r ik e .
Qn th e so u th s id e o f th e e a s t - s t r i k i n g f a u lt, h o w e v e r ,
J u r a s s i c s t r a t a a r e p r e s e n t and p c c u r a p p r o x im a t e ly at th e h o r iz o n
e x p e c t e d if t h e y a r e to b e c o n tin u o u s w ith e q u iv a le n t J u r a s s i c s t r a t a on
th e o p p o s ite s id e of th e r id g e (i. e . , in th e Sou th C o tto n w o o d C r e e k
d r a in a g e ).
T h is s u g g e s t s th a t thq S ou th C o tto n w o o d C r e e k fa u lt d o e s n o t
r e t a in i t s n o r t h w e s t s t r ik e b e n e a th th e v o lc a n ic r o c k a s th e r e i s
a p p a r e n tly l i t t l e or no s t r a t ig r a p h ic d is p la c e m e n t a c r o s s s u c h a tr e n d .
The s o u th w e s t tr e n d in g fa u lt r a d ia tin g fr o m th e ju n c tio n i s a r e v e r s e
fa u lt (up on th e s o u th e a s t , dow n o^i th e n o r th w e s t) th a t e x h ib it s a s m a ll
c o m p o n e n t of l e f t - l a t e r a l s t r i k e - s l i p m o v e m e n t .
«1
It d ip s s t e e p ly to th e
68
s o u th e a s t, h a s a s t r a t ig r a p h ic d is p la c e m e n t of a p p r o x im a t e ly 150 f e e t ,
an d a s o u th w e s t t e r m in a t io n n e a r S ou th C o tto n w o o d C r e e k . , T h e m in im a l
d is p la c e m e n t and th e r a t h e r a b ru p t t e r m in a t io n o f t h is fa u lt in d ic a te th a t
it is h ot th e c o n tin u a tio n o f th e South C o tto n w o o d C r e e k fa u lt.
T he
s t r a t ig r a p h ic d is p la c e m e n t on th e e a s t t r e n d in g fa u lt, h o w e v e r , i s fa r
in e x c e s s of th a t of th e s o u th w e s t t r e n d in g fa u lt and c o m p a r e s fa v o r a b ly
w ith th a t o f th e -S o u th C o tto n w o o d C r e e k fa u lt. . T h e e a s t tr e n d in g fa u lt,
t h e r e f o r e , is m o s t li k e l y a c o n tin u a tio n of th e South C o tto n w o o d C r e e k
fa u lt.
It i s sh o w n a s a v e r t i c a l fa u lt b e c a u s e e v id e n c e i s in s u f f ic ie n t
to v e r i f y i t s in c lin a t io n .
T h e fa u lt c o u ld b e t r a c e d np f a r t h e r e a s t th an
the. S E 1 /4 . s:eCi 3 2 , . T . 3 S . , . R . ' 6 'E.
S e d im e n ta r y •s t r a t a lo c a t e d in s e c . 31 a n d E 1 /2 s e c . . 35,, T. 3 S . ,
R . 5 -E . , o c c u r on th e up'throw n s id e o f th e Sou th C o tto n w o o d C r e e k
fa u lt and c o m m o n ly dip to th e so u th an d s o u th w e s t.
A n e x c e p t io n to
th e c o m m o n .d ir e c t io n of d ip o c c u r s in s e c . 31, T . 4' S, ,. R . 6 E . , w h e r e
th e U p p e r C a m b r ia n P i l g r i m and R e d .L ion f o r m a t io n s a r e d e fo r m e d in to
a s o u th e a s t p lu n g in g s y n c lin e ; th e s y n c lin e i s t r u n c a te d on th e so u th b y
th e e a s t tr e n d in g p a r t of th e South C o tto n w o o d C r e e k fa u lt. . A c r o s s s e c t io n of the s y n c lin e i s sh o w n b y W. M . W eb er (1 9 6 5 , U npub. M. S.
T h e s i s , M on t.- S ta te U n iv . , B o z e m a n , p . 4 9 ).
A ls o , a fe w b e d s of the
L o d g e p o le L im e s t o n e a r e o v e r tu r n e d a d ja c e n t to th e S ou th C o tto n w o o d
C r e e k fa u lt in th e E 1 /2' SW 1 /4 s e c . 3 6 , T: 3 S. , R 5 E ,
T h e s e d ata
s u g g e s t th a t th e s t r a t a in th e a b o v e m e n t io n e d s e c t io n s h a v e b e e n m o v e d
s o u th w e s tw a r d (a s a u n it), a s w e ll a s h a v in g b e e n t h r u s t u p w a rd .
The
I
I
I
69
th r o w o f th e S o u th C o tto n w o o d C r e e k fa u lt i s s e c . 3 5 , T . 3>S. , R . S E . ,
is a p p r o x im a t e ly 1600 f e e t and th e in c lin a t io n i s b e li e v e d to b e s te e p ,
in d ic a tin g th a t s o u th w e s tw a r d t r a n s lo c a t io n of th e s t r a t a i s n ot g r e a t.
- S e d im e n t a r y s t r a t a so u th of th e e a s t tr e n d in g e x t e n s io n o f th e
S ou th C o tto n w o o d C r e e k fa u lt a r e s t r o n g ly fa u lte d , fo ld e d , b r e c c ia t e d ,
s i l i c i f i e d , and p a r t ia l ly c o v e r e d b y v o lc a n ic s t r a t a .
I n te r p r e t a t io n s
of th e s t r u c t u r a l and s t r a t ig r a p h ic r e la t io n s h ip s a r e , fo r th e m o s t p a r t,
b a s e d on a m in im u m ( if n o t a n in s u ffic ie n t)' a m o u n t o f d a ta and a r e
t h e r e f o r e h ig h ly c o n j e c t u r a l.
T h e s e r i e s o f f a u lt s e x is t in g in t h is a r e a
m a y b e s p la y f a u lt s w h ic h r e p r e s e n t th e s o u th e a s t t e r m in a t io n o f th e
S o u th 'C o tto n w o o d C r e e k fa u lt.
S tr a ta e x p o s e d w e s t o f fa u lt I ( fig u r e 5, b o th c r o s s - s e c t i o n s ) a r e
' " t ..
k n ow n t o b e o v e r tu r n e d to th e w e s t .
T h a t th e fa u lt d ip s s t e e p ly to th e
e a s t in n ot c e r t a in , b u t th e d ip and r e l a t iv e m o v e m e n t in d ic a t e d a r e
c o n s is t e n t w ith o th e r s t r u c t u r a l d a ta of th e m a p a r e a .
In b o th i n t e r ­
p r e t a t io n s (fig u r e 5 , a , b ), a s a u n it a ll s t r a t a e a s t of fa u lt I e x h ib it
a r e v e r s e r e la t io n s h ip to th e fo o t w a ll b lo c k . . T h e r e l a t iv e a m o u n t of
m o v e m e n t a lo n g in d iv id u a l f a u lt s v a r i e s .
F i e l d e v id e n c e s u g g e s t s th a t th e M is s io n C a n y o n a n d 'A m sd e n s t r a t a
in th e N E 1 /4 s e c . 6 , T . 4 S. , R. 6' E . , m a y b e o v e r tu r n e d to th e so u th .
P r o o f o f th e o v e r tu r n in g i s la c k in g b e c a u s e of e x t e n s iv e d e fo r m a tio n o f
th e s tr a t a , b u t f ig u r e 5 a s h o w s a p o s s i b l e r e la t io n s h ip if t h is i s th e
case.
T h e d if f ic u lt y w ith th e in t e r p r e t a t io n a r i s e s a lo n g fa u lt 2; th e
u p w a rd m o v e m e n t o f s t r a t a e a s t of th e fa u lt i s not c o n s is t e n t w ith th e
70
I
A- Reverse foulting
B-Verticol foulting
C- Erosion
Plon view
F ig u r e 6 . D ia g r a m m a t ic il lu s t r a t io n of d e v e lo p m e n t of th e S o u th C o tto n w o o d
C r e e k fa u lt at i t s in t e r s e c t io n w ith th e W h e e le r G u lch fa u lt.
71
d r a g e x h ib ite d b y - s t r a t a on th e w e s t s id e o f th e fa u lt.
F ig u r e 5b
s h o w s a n o th e r in t e r p r e t a t io n , w h ic h a s s u m e s th a t th e M is s io n .C a n y o n
and A m s d e n s t r a t a a r e n o t o v e r tu r n e d .
In th is in t e r p r e t a t io n th e
d r a g e x h ib ite d a lo n g fa u lt 2a i s n ot in c o n s is t e n t w ith th e d ir e c t io n o f
m o v e m e n t in d ic a t e s .
B o th in t e r p r e t a t io n s a r e c o n s is t e n t w ith lo c a l
an d r e g io n a l s t r u c t u r a l d a ta .
F ig u r e 5b i s th e m o r e a c c e p t a b le in
th a t it i s th e l e a s t s p e c t a c u la r in t e r m s of " s t r u c t u r a l g y n a s t ic s . "
B y c o n t r a s t , th e d e fo r m a tio n n o r th of th e e a s t tr e n d in g e x t e n s io n o f th e
S ou th C o tto n w o o d C r e e k fa u lt is m u c h l e s s th a n th a t so u th of it; th e
in t e r p r e t a t io n r e q u ir e d fo r f ig u r e 5 a , t h e r e f o r e , i s a l s o r e a s o n a b le .
U n d isr u p te d T e r t i a r y v o lc a n ic r o c k s in p a r t o v e r lie th e s o u th w e s t
tr e n d in g fa u lt (in S o u th C o tto n w o o d C r e e k d r a in a g e ), th e S o u th C o tto n w o o d
C r e e k fa u lt and th e e a s t tr e n d in g e x t e n s io n of it (in c lu d in g th e s p la y
f a u lt s ) .
,
T h e v o lc a n ic r o c k s a r e p o s t - l a t e e a r l y F o c e n e in a g e , and
m o v e m e n t on th e fa u lts m u s t h a v e c e a s e d p r io r to t h e ir d e p o s itio n .
. S t r u c t u r e s a s s o c i a t e d w ith th e S o u th C o tto n w o o d fa u lt:
A lo n g th e
S o u th C o tto n w o o d C r e e k fa u lt a s e r i e s of m in o r t h r u s t f a u lt s i s d e ­
v e lo p e d e a c h of w h ic h d ip s to w a r d th e m a in fa u lt.
C r o s s -s e c tio n
C - C 1 (p la te I) s h o w s a g ro u p of im b r ic a t e d th r u s t fa u lts o c c u r r in g in
s e c . 3 5 , T . 3 'S. ,. R.' 5 'E ; th e d ip of e a c h u p w a rd s u c c e e d in g fa u lt i s
s t e e p e r th a n th a t of- a n y -fault b e lo w it .
T h e th r u s t s l i c e s w e r e a p p a r e n ­
t l y b r o u g h t up a s d r a g p h e n o m e n a a lo n g th e South C o tto n w o o d C r e e k
fa u lt.
72
In th e w e s t - c e n t r a l p a r t of s e c . 3 2 , T. 3 S. ,. R . 6 'E . , a s m a ll
le a d d e p o s it i s p r e s e n t in P r e Cam brian, m e t a m o r p h ic r o c k .
A s m a ll
fa u lt o c c u r s so u th o f th e d e p o s it in - s e d im e n t a r y s t r a t a and m a y ex te n d
in to th e m e t a m o r p h ic r o c k , th u s a ffo r d in g a w e a k n e s s z o n e a lo n g w h ic h
th e le a d d e p o s it f o r m e d .
C r o s s F a u lt s
D e v e lo p in g s im u lt a n e o u s ly o r p o s s i b l y (in p a rt) s o m e w h a t e a r l ie r
th a n th e Sou th C o tto n w o o d C r e e k fa u lt w a s th e W h e e le r M o u n ta in m o n o r
c lin e , s o n a m e d (h e r e in ) fo r it s p r o m in e n t e x p o s u r e on th e s o u th e a s t
s id e of th a t m o u n ta in ( s e c . 2 an d 11, T. 4 S. ,. R. 5 ' E ..) On th e s o u th ­
w e s t s id e o f th e m o u n ta in th e b e d s dip g e n t ly to th e n o r t h e a s t , b e g in to
i n c r e a s e in d ip (n o r th e a s t) n e a r it s c r e s t , and th e n l e s s e n to a g e n tle
n o r t h e a s t d ip a g a in on th e fla n k s o f th e m o u n ta in n e a r S o u th C o tto n w o o d
C reek.
A s s o c i a t e d w ith th e m o n o c lin e i s a s e r i e s o f t r a n s v e r s e fa u lts
th a t a r e o r ie n te d a p p r o x im a t e ly p e r p e n d ic u la r to th e a x is of th e fo ld
an d in p a r t o w e t h e ir d e v e lo p m e n t to d if f e r e n t d e g r e e s o f fo ld in g of th e
m o n o c lin e .
, A d ja c e n t to W h e e le r G u lch ( s e c . 2 -anti 11, T . 4 S. , - R . . 5 E . ). i s
a fa u lt th a t tr e n d s s o u t h - s o u t h w e s t an d i s h e r e n a m e d th e W h e e le r
G u lc h fa u lt.
In s e c . 3 6 , T . 3 S. ,. R. 5 E,. , t h is fa u lt t r a n s e c t s the
S o u th -C o tto n w o o d C r e e k fa u lt an d , a s n o te d e a r l i e r , th e m in im u m
s t r a t ig r a p h ic d is p la c e m e n t on th a t fa u lt i s d if f e r e n t on o p p o s ite s id e s
of th e W h e e le r G u lc h fa u lt.
T h e W h eeler G u lc h fa u lt p la n e (in; s e c . 36)
i s a p p a r e n tly v e r t i c a l and e x h ib it s a s t r a t ig r a p h ic d is p la c e m e n t of
!
73
a p p r o x im a t e ly 400 f e e t .
Q u ad ran t Q u a r tz ite o f th e u p th r o w n (n o r th e r n )
b lo c k i s e q u a l in e le v a t io n to J u r a s s i c s t r a t a o f th e d o w n d r op p ed b lo c k .
A p la n v ie w o f th e s t r u c t u r e in s e c t io n 36 s u g g e s t s th a t t h e r e m a y b e a
s m a ll c o m p o n e n t of r i g h t - l a t e r a l s t r ik e - s lip m o v e m e n t d e v e lo p e d a lo n g
th e W h e e le r G u lch f a u lt.
:
I,
H o w e v e r , t h is a p p a r e n t m o y e m e n t can a ls o
b e e x p la in e d b y v e r t i c a l d is p la c e m e n t on th e s a m e fa u lt,, a s i s illu s t r a t e d
in f ig u r e 6 .
A c t u a lly b o th t y p e s of m o v e m e n t m a y e x i s t , but th e d ip -
s lip i s b e li e v e d b y t h e w r it e r to b e b y f a r th e m o r e s ig n if ic a n t .
T h e t h ic k n e s s o f th e Q u a d ra n t n o r t h w e s t o f th e fa u lt i s 300 f e e t ,
w h e r e a s it i s o n ly 200 f e e t th ic k on th e s o u th e a s t s id e ; th e A m s d e n
!
F o r m a t io n e x h ib it s a s i m i l a r r e la t io n s h ip .
I
T h is s u g g e s t s th a t th e
W h e e le r G u lc h fa u lt w a s a c t iv e in P e n n s y lv a n ia n t im e and th a t s u b s e ­
q u e n tly L a r a m id e fa u ltin g d e v e lo p e d along a p r e - e x i s t i n g s t r u c t u r a l
tr e n d .
M c M a n n is (1 9 5 5 ) h a s n o te d .s im ila r o c c u r r e n c e s f o r P e n n s y l ­
v a n ia n a s w e l l a s o th e r s t r a t a in th e B r id g e r R a n g e , and A lp h a and
F a n s h a w e (1 9 5 4 ) and S o n n e b e r g (1 9 5 6 ) h a v e a ls o fou n d e v id e n c e to i n ­
d ic a t e m in o r P a l e o z o i c (an d M e s o z o ic ), m o v e m e n t on p r e s e n t d ay
s t r u c t u r a l tr e n d s in c e n t r a l and s o u t h - c e n t r a l M ontana.
F a r t h e r to th e n o r t h e a s t (i. e . , n o r t h e a s t of th e Sou th C otton w ood
C r e e k fa u lt) th e W h e e le r G u lch fa u lt e n t e r s P r e c a m b r ia n m e t a m o r p h ic
r o c k , b u t c o u ld n o t b e t r a c e d f a r t h e r b e c a u s e of th e h e a v y o v e r g r o w th
an d la c k of o u t c r o p s .
A d ja c e n t to W h e e le r G u lch and n e a r th e s o u th e r n m a r g in of the m a p
a r e a , th e fa u lt i s v e r t i c a l and a g a in e x h ib it s a s t r a t ig r a p h ic d is p la c e m e n t
I
74
o f a p p r o x im a t e ly 400- f e e t ; Ip w e r L o d g e p o le -L im e s to n e on th e u p th ro w n
(n o r th e r n ) b lo c k l i e s a g a in s t u p p e r L o d g e p o le L im e s t o n e o f th e d o w n d r o p p e d b lo c k .
S o u th w e s t o f the m a p a r e a (in th e G a r n e t M o u n ta in
q u a d r a n g le ) M c M a n n is an d C h a d w ick (1 9 6 4 ) m a p p e d th e s o u th w e s t
e x t e n s io n o f th e W h e e le r G u lch fa u lt.
T h ere (se c .
10,
11, 14, 15,
T-:- 4 -S . ,. R . 5' E.-) it c h a n g e s fr o m a v e r t i c a l fa u lt to a n o r t h w e s t
s t r ik in g - n o r t h e a s t d ip p in g t h r u s t f a u lt, w h ic h im p lie s a m in o r l e f t la t e r a l c o m p o n e n t o f S t r ik q v s lip m o v e m e n t on th e m a in n o r t h - n o r t h ­
e a s t p a r t o f th e fa u lt.
F o ld in g a lo n g th e m o n o c lin e s e e m s to b e m o r e in t e n s e on th e s o u th ­
e a s t s id e o f th e W h e e le r G u lc h fa u lt th a n on th e n o r t h w e s t s id e .
Thus
g r e a t e r t h r u s t d is p la c e m e n t on th e n o r t h w e s t s id e of tb e fa u lt co u ld b e
c o m p e n s a te d b y th e t ig h t e r fo ld in g ( g r e a t e r s h o r te n in g ) p r e s e n t on th e
s o u th e a s t s id e .
N o r th w e s t o f th e W h e e le r G u lch fa u lt i s -a n o r m a l f a u lt th a t d ip s
to th e n o r th w e s t and t r e n d s s o u th w e s t , t r a n s e c t in g s e c .
4 S. ,. R . S E , ,. and s e c . 3 5 , T . 3 S. ,. R . S E .
9, 3, 2, T-.
In s e c t io n 9 F r e o a m b r ia n
m e t a m o r p h ic r o c k (u p th rp w n b lo c k ) i s e m p la c e d a g a in s t M e a g h e r L i m e s t o n e , w h e r e a s in s e c tio p . 3 (at th e h e a d of D r y G u lch) u p p e r M is s io n
C a n y o n L im e s t o n e o f th e d o w n d ro p p ed ( n o r th w e s te r n ) b lo c k l i e s a g a in s t
u p p e r L o d g e p o le L im e s f o n e o f th e u p th r o w n b lo c k .
T h e s t r a t ig r a p h ic
d is p la c e m e n t a t e a c h lp p a tio n i s a p p r o x im a t e ly 350 f e e t . . T h e fa u lt
a p p a r e n tly d ie s out in th e SW 1 /4 s e c . 3 5 , T . 3 S. , R . 5 E . , a s "it
d o e s n o t e x i s t n o r t h e a s t o f S o u th C o tto n w o p d C r e e k .
U n d is tu r b e d
75
E o c e n e v o lc a n ic r o c k c o n c e a ls th e fa u lt to th e s o u th w e s t (S j s e c . 9,
T . 4 S. , R . 5 E . ), in d ic a tin g th a t m o v e m e n t on th e fa u lt c e a s e d p r e - .
v io u s to th a t t im e .
R e v e r s e d r a g o c c u r s on b o th s id e s o f th e fa u lt (in
th e N E
3, T." 4 S. ,. R . S E . ) an d i t s o r ig in w ill b e d i s ­
SW j s e c .
c u s s e d w ith th a t of th e n e x t fa u lt to th e n o r t h w e s t .
. T r a n s e c t in g th e m o n o c lin e on e m i l e fa r t h e r to th e n o r t h w e s t i s a
r e v e r s e fa u lt th a t t r e n d s s o u th w e s t in s e c .
33, 3 4 , T . 3 S. , R . 5 'E. ,
c h a n g in g tr e n d to n e a r ly d ue so u th in s e c . 4 , T . 4 :S . ., - R . 5 E . . T he
fa u lt d ip s s t e e p ly to th e n o r t h w e s t and h a s a s t r a t ig r a p h ic d is p la c e m e n t
o f a p p r o x im a t e ly 5 5 0 f e e t in th e N E ^ s e c . 33.
A t t h is lo c a t io n u p p er
J e f f e r s o n L im e s t o n e o f th e u p th r o w n (n o r th w e s te r n ) b lo c k l i e s a g a in s t
lo w e r M is s io n C a n y o n L im e s t o n e o f th e d o w n th ro w n b lo c k . . F a r t h e r to
th e n o r t h e a s t th e fa u lt p r o b a b ly c o n n e c t s w ith th e S ou th C o tto n w o o d
C r e e k fa u lt, b u t v a l l e y a llu v iu m and c o llu v iu m (in SW ^ s e c . 27, T . 3 S . ,
R . 5 E . ) c o n c e a l a n y s u c h c o n n e c tio n .
T h e so u th en d o f th e fa u lt is
c o n c e a le d b y u n d is tu r b e d E o c e n e v o lc a n ic r o c k , in d ic a tin g a m in im u m
a g e fo r m o v e m e n t on th e fa u lt.
R e v e r s e d r a g i s e x h ib ite d on th e d o w n d r opped ( s o u th w e s t) s id e of
th e fa u lt in s e c . 33, an d o c c u r s on t h e o p p o s ite end o f th e s a m e b lo c k fo r
w h ic h r e v e r s e d r a g w a s n o te d a lo n g th e n o r m a l fa u lt p r e v io u s ly
d e s c r ib e d .
F ig u r e 7 i s a s k e t c h o f th e r e la t io n s h ip of r e v e r s e d ra g
to th e s t r a t ig r a p h ic d is p la c e m e n t a lo n g th e tw o f a u lt s .
T h e b lo c k
b o r d e r e d b y -the tw o . f a u lt s m a y h a v e m o v e d u p w a rd a d ju s tin g i t s e l f a fte r
th e m a in p h a s e of fa u ltin g o c c u r r e d .
M o tio n .of th e b lo c k wouj-d n o t h a v e
b e e n e n t ir e ly v e r t i c a l b u t s lig h t ly to th e s o u th e a s t,, to o , a s g u id ed b y
76
th e a lr e a d y e x is t in g f a u lt s .
NW
SE
W
$
F ig u r e 7. S k e tc h of r e v e r s e d r a g r e la t io n s h ip s a lo n g tw o
c r o s s f a u lt s .
T h e n o r t h w e s t e r n m o s t of th e f a u lt s t r a n s e c t in g th e m o n o c lin e o c c u r s
in s e c . 2 8 , 32, 33, T . 3 S. , R . 5 E .
In s e c t io n s 28 and 33 it tr e n d s
s o u th w e s t and i s a n o r m a l fa u lt d ip p in g s t e e p ly to th e n o r th w e s t.
In th e
SW ^ NW ^ s e c . 3 3 , th e s t r a t ig r a p h ic d is p la c e m e n t is a p p r o x im a t e ly
500 fe e t; b a s a l s t r a t a of the L o d g e p o le L im e s t o n e o f th e d o w n d ro p p ed
(n o r th w e s t) b lo c k a r e a d ja c e n t to th e lo w e r p a r t of th e P i lg r i m L im e s t o n e
of th e u p th ro w n b lo c k .
In s e c t io n 32 th e fa u lt c h a n g e s to a m o r e w e s t e r l y
s t r ik e , m a in ta in in g it s n o r m a l fa u lt a ttitu d e w ith th e fa u lt p la n e d ip p in g
s t e e p ly to th e n o rth .
L it t le B e a r C r e e k F a u lt and R e la te d S t r u c t u r e s
T he l i t t le B e a r C r e e k fa u lt, h e r e n a m e d fo r it s p r o x im it y to th a t
s t r e a m , tr e n d s n o r t h w e s t and is a p p a r e n tly o f h ig h a n g le r e v e r s e n a tu re,
a s s u g g e s t e d b y o v e r tu r n e d s t r a t a on th e d o w n d ro p p ed s id e o f th e fa u lt.
T h e m in im u m s t r a t ig r a p h ic d is p la c e m e n t i s a p p r o x im a t e ly 800 f e e t w ith
M e a g h e r L im e s t o n e o f th e d o w n d ro p p ed (s o u th w e s t) b lo c k in c o n ta c t w ith
P r e c a m b r ia n m e t a m o r p h ic r o c k of th e u p th ro w n b lo c k .
of th e fa u lt i s b u r ie d b y v o lc a n ic r o c k .
T h e s o u th e r n p a r t
T h e fa u lt a p p a r e n tly c o n tin u e s
s o u th e a s tw a r d b e n e a th th e v o lc a n ic c o v e r a s s u g g e s t e d b y th e s im il a r it y of
r e l a t io n s h ip s o f th e P a l e o z o i c and P r e c a m b r ia n r o c k s in s e c s . 7 and 8 ,
)
77
T . 4 'S. , R . S E .
T h e v o lc a n ic r o c k i s u n d is tu r b e d and i s of E o c e n e a g e ,
in d ic a tin g th a t m o v e m e n t on th e fa u lt q e a s e d p r io r to th a t t im e .
T w o s o u th w e s t tr e n d in g fa u lts a r e a s s o c i a t e d w ith th e L it t le B e a r
C r e e k fa u lt.
T h e s o u th e r n m o s t , in s e c . 7, T . 4 S. , R . S E . ,
i s c o n s id -
I
e r e d a v e r t i c a l fa u lt a s f ie l d e v id e n c e i s in s u f f ic ie n t to d e t e r m in e it s
in c lin a tio n .
S t r a t ig r a p h ic d is p la c e m e n t on th e fa u lt i s a p p r o x im a t e ly
I
200 f e e t , w ith P r e c a m b r ia n m e t a m o r p h ic r o c k of th e u p th r ow n .(n o rth w est)
;
s id e a d ja c e n t to lo w e r M e a g h e r L im e s t o n e of th e d o w n d ro p p ed b lo c k .
T h e o th e r m o r e w e s t e r l y t r e n d in g fa u lt in s e c . 6 , T . 4 S.
and s e c . I, T . 4 S.
R. S E . ,
'
I
R . 4 E . , e x h ib it s a n o r m a l r e la t io n s h ip , w ith th e
fa u lt p la n e d ip p in g s t e e p ly to th e n o r th .
N e a r W ills o n C r e e k th e s t r a t i ­
g r a p h ic d is p la c e m e n t i s a p p r o x im a t e ly 4 0 0 f e e t , w ith P r e c a m b r ia n
m e t a m o r p h ic r o c k o f th e u p th r ow n (s o u th e r n ) b lo c k a g a in s t M e a g h e r
L im e s to n e of th e d o w n d ro p p ed b lo c k .
!
N e a r L it t le B e a r C r e e k th e r e la tio n ­
sh ip i s n ot c l e a r , b u t th e d is p la c e m e n t a p p e a r s to b e l e s s and m a y n o t
e x c e e d 100 f e e t .
T h e fa u lt c o u ld n o t b e t r a c e d in to th e m e t a m o r p h ic r o c k so u th o f
W ills o n C r e e k , b u t tw o l i n e s of e v i c e n c e s u g g e s t th a t it m a y e x i s t th e r e :
(I) a d r a w i s p r e s e n t in th e m e t a m o r p h ic r o c k a lo n g th e p r o j e c t io n of th e
f a u lt ; and ( 2 ) a r e v e r s a l in d ip o f th e f o li a o c c u r s a c r o s s th e p r o j e c t io n
o f th e fa u lt in th e g E ^ s e c . .2 , T . 4 S . ,. R . 4 E .
T h e n o r t h e a s t t e r m in u s
o f th e fa u lt s e e m s t o beat, th e ju n c tio n w ith th e L it t le B e a r C r e e k fa u lt.
C o n n e c tio n of t h is fa u lt w ith th e n o r t h e a s t tr e n d in g fa u lt in th e N E ^ s e c . 6 ,
T . 4 S. , R . 5- E . , d o e s n o t a p p e a r to b e v a lid b e c a u s e :
(I) th e tw o fa u lts
a r e n o t c o n tin u o u s , b u t in t e r s e c t th e L it t l e B e a r C r e e k fa u lt a t d if f e r e n t
..
1
78
p la c e s ; an d (2) th e n o r t h e a s t s t r ic k ip g fa u lt (N E ^ s e c .
6, T . 4 S. ,
R . S E . ) and th a t p a r t o f th e L it t le B e a r C r e e k fa u lt n o r th of it s
ju n c tio n w ith th e la t t e r fa u lt w e r e a p p a r e n tly a c t iv e in th e Q u a te r n a r y .
T h is i s s u g g e s t e d b y th e p r e s e r v a t i o n o f la n d s lid e m a t e r i a l in th e N E j
sec.
6 , T . 4 S. , R . S E . , and in E ^ s e c . 31 and W j s e c .
R. 5 E.
32, T . 3-S. ,
T h e la n d s lid e d e b r is i s a p p a r e n tly p r e s e r v e d on th e d o w n d ropped
s id e s of t h e s e tw o f a u lt s .
(T h is in d ic a t e s a r e v e r s a l in m o v e m e n t fo r
th a t p a r t o f th e L it t le B e a r C r e e k fa u lt b e in g d is c u s s e d .')
A s s o c i a t e d w ith th e L it t le B e a r C r e e k fa u lt i s a s y n c lin e , th e a x is of
w h ic h t r e n d s n e a r ly p a r a ll e l to th e fa u lt.
T h e s e d im e n t a r y s t r a t a o f th e
s o u th w e s t e r n lim b o f th e s y n c lin e h a v e b e e n t ilt e d in u n ity w ith underlying
b a s e m e n t b lo c k s , e x c e p t w h e r e in flu e n c e d b y th e a fo r e m e n tio n e d
s o u th w e s t and w e s t tr e n d in g f a u lt s . - S tr a ta of th e n o r t h e a s t e r n lim b h a v e
b e e n tu r n e d up s h a r p ly and s lig h t ly o v e r tu r n e d a lo n g th e L it t le B e a r Creek
fa u lt.
T h e L it t le B e a r C r e e k f a u lt , th e s y n c lin e , and th e tw o t r a n s v e r s e
■faults h a v e a c l o s e l y r e la t e d h is t o r y o f d e v e lo p m e n t. - A s s t r e s s w a s
a p p lie d fr o m th e e a s t - n o r t h e a s t , th e n o r t h e a s t b lo c k o f th e L it t le B e a r
C r e e k fa u lt w a s t h r u s t u p w a rd and s t r a t a o f th e dow n d r o p p ed b lo c k w e r e
s im u lt a n e o u s ly b e in g d e f o r m e d to p r o d u c e a s y n c lin a l s t r u c t u r e .
The
s o u th w e s t tr e n d in g fa u lts p r o b a b ly d e v e lo p e d c o n c u r r e n t ly , due to
d if f e r e n t ia l s t r e s s d e v e lo p e d d u rin g th e c o m p r e s s io n and m o v e m e n t on
th e L it t le B e a r C r e e k fa u lt.
79
G a lla tin R a n g e F r o n t F a u lt
One of th e m o s t s ig n if ic a n t s t r u c t u r e s in th e m a p a r e a i s th e G a lla tin
R ange fr o n t fa u lt or fa u lt z o n e .
H a c k e tt and o t h e r s (I9 6 0 , p., 50) and
. R o b in s o n (1961, p. 1009) s t a t e th a t th e n e c e s s a r y d a ta to p r o v e th e
e x i s t e n c e o f t h is fa u lt i s la c k in g , b u t th e p r e s e n t w r it e r d o e s n ot c o n c u r .
T h e fo llo w in g l i n e s of e v id e n c e s u g g e s t th a t th e fa u lt d o e s e x is t :
(I) th e
tr e n d o f th e m o u n ta in fr o n t i s lin e a r ; ( 2) la n d s lid e d e b r is i s c o n c e n tr a te d
a lo n g th e m o u n ta in fr o n t; (3), m u c h of th e la n d s lid e m a t e r i a l p r e s e r v e d
a lo n g th e m o u n ta in fr o n t i s c o m p r is e d of v o lc a n ic r o c k ,^ y e t su c h r o c k i s
c o m m o n ly a b s e n t in th e im m e d ia t e ly a d ja c e n t m o u n ta in r a n g e , th u s
s u g g e s t in g .p r e s e r v a t io n on th e d o w n d ro p p ed b lo c k ; (4) p r e - T e r t i a r y
o u tc r o p s a r e v ir t u a l ly a b s e n t in th e b a s in p r o p e r , in d ic a tin g th a t th e
o ld e r r o c k m u s t li e a t c o n s id e r a b le d e p th b e lo w the. T e r t i a r y and y o u n g e r
m a t e r i a l s of th e b a s in ; (5)" T e r t i a r y s t r a t a l o c a l l y abut a g a in s t th e m o u n ­
ta in fr o n t w ith a s t e e p p la n e of c o n ta c t .(SE ^ s e c . 29,. T . 3 S. ,. R . 5 E . );
( 6 ) p r e - T e r t i a r y s t r a t a o f th e m o u n ta in r a n g e g e n e r a lly d ip g e n tly to th e
n o r t h e a s t , b u t n e a r th e r a n g e fr o n t ( s e c .
3 2 , 3 5 , and 3 6 , T . 3 S. ,
R . 4 E . ) th e d ip i n c r e a s e s and c h a n g e s d ir e c t io n s o .t h a t it i s to w a r d th e
p r o p o s e d fa u lt; (7) M. D . M ifflin (1963,. U npub. M. S . T h e s i s , M ont.
S ta te U n iv . , B o z e m a n ) h a s sh o w n th at c o n s id e r a b le v e r t i c a l d is p la c e m e n t
o f r o c k s h a s o c c u r r e d , a lo n g th e s u g g e s t e d fa u lt t r e n d w e s t o f th e m a p
a r e a ; (8 ) M c M a n n is and C h a d w ick (1964) sh o w h o r iz o n t a l o f f s e t of th e
S q u aw C r e e k - C h e r r y C r e e k fa u lt, th e d is p la c e m e n t o c c u r r in g a lo n g th e
s a m e r a n g e fr o n t tr e n d ; (9) in th e SW
s e c . 14, SE ^ s e c . 15, and th e N E
80
s e c . 22 , T . 3 S. , R . 5 ' E . ,, e v id e n c e in d ic a t e s th a t P r e c a m b r ia n m e t a m Or­
p h ic r o c k h a s b e e n d is r u p te d b y th e fa u lt pr a b r a n c h of it.
M e ta m o r p h ic
r o c k in th e d is r u p t e d zo n e i s h ig h ly s h e a r e d , f r a c t u r e d , an d c o n to r te d .
F o l i a o f th e s o u t h e a s t b lo c k d ip 7 0 ° to th e s o u th e a s t w h e r e a s f o lia on th e
o p p o s ite s id e d ip a p p r o x im a t e ly 10° n o r t h e a s t , . s t r o n g ly s u g g e s t in g
fa u ltin g .
A ls o , a r e m n a p t o f v o lc a n ic r o c k (n ot la n d s lid e d e b r is ) 'i s
p r e s e r v e d on th e d o w n d ro p p ed (n o r th w e s t) b lo c k ; (10) s t r ic k in g p a r a ll e l
to th e t r e n d of t h e s u g g e s t e d fa u lt and n o r t h w e s t o f it , a s u b s u r f a c e fa u lt
h a s b e e n d e t e c t e d th r o u g h th e u s e o f g r a v it y an d m a g n e t ic d a ta ( D a v is and
o t h e r s , 1965).
T h e n o r t h e a s t t r e n d in g G a lla tin R a n g e ,f r o n t fa u lt e x t e n d s fr o m th e
s o u th e r n m a r g in o f-S p a n ish C r e e k V a lle y (s o u th w e s t of th e m a p a r e a ) to
th e m o u th o f B e a r C a n y o n n o r t h e a s t of th e m a p a r e a .
T h e fa u lt i s at
l e a s t 23 m i l e s lo n g , f o r m in g th e m u tu a l b o u n d a r y of th e G a lla tin .R a n g e ,
th e G a lla tin V a lle y , a n d th e T e r t i a r y d e p o s it s of th e la t t e r .
T h e fa u lt h a s
a "norm al r e la t io n s h ip an d d ip s s t e e p ly t o th e n o r t h w e s t . • S tr a ta of th e
u p th r ow n b lo c k r a n g e f r o m P r e c a m b r ia n to E o c e n e ( v o lc a n ic r o c k o f th e
T o m L a y P r a r i e a r e a ) , and t h o s e xOf th e d o w n th ro w # b lo c k ra n g e fr o m
M io c e n e to R e c e n t e x c e p t:
(I) on th e s b u th w e s t en d o f th e fa u lt w h e r e
T e r t i a r y v o lc a n ic r o c k and P r e c a m b r ia h m e t a m o r p b ic r o c k a r e a ls o on
th e d o w n d ro p p ed s id e , and (2) a t th e m o u th of "Middle C r e e k (SW ^ se c . 14,
an d SE ^ s e c . 15, T . 3 S.
R . 5 E . ) w h e r e a s liv e r of P r e c a m b r ia n
m e t a m o r p h ic r o c k i s d o w n d ro p p ed r e l a t iv e to th e m a in m o u n ta in m a s s
(but i s s t i l l up,throw n r e l a t i v e to fh e b a s in ) .
L
81
M a r tin D . M ifflin (1963, U npub. M . S. T h e s is ,. M on t. S ta te U n iv . ,
-B o z e m a n ) e s t im a t e d s t r a t ig r a p h ic d is p la c e m e n t on th e fa u lt to b e
b e tw e e n 1500 f e e t and 2 5 0 0 f e e t n e a r th e m o u th of G a lla tin C an yon , w e s t
of th e m ap a r e a .
H is e x t im a t e i s b a s e d on th e s i m i l a r i t y o f tw o v e r t i c a l ­
ly o f f s e t s u r f a c e s b e a r in g b a s i c v o lc a n ic r e m n a n t s .
b e g r e a t e r on tire n o r t h e a s t en d of th e fa u lt.
D is p la c e m e n t m a y
P e a l e (1896) p o s tu la te d
e a s t w a r d t il lin g o f th e b a s in to e x p la in th e e a s t w a r d dip pf th e T e r t ia r y
stra ta
t h e r e in .
R o b in s o n (1961,. p. 1009) n o te d th a t o ld e r T e r t i a r y r o c k s
d o m in a te th e w e s t e r n h a lf o f th e b a s in w h e r e a s th e e a s t e r n h a lf i s
d o m in a te d b y y o u n g e r T e r t i a r y s t r a t a .
H e a ttr ib u te d t h is to r e c u r r e n t
t ilt in g o f th e b a s in , w h ic h s u g g e s t s g r e a t e r d is p la c e m e n t on th e n o r t h e a s t
en d o f th e G a lla tin R a n g e fr o n t fa u lt.
T h e r a n g e fr o n t fa u lt a p p a r e n tly e x h ib it s a l e f t - l a t e r a l c o m p o n e n t
of s t r i k e - s l i p m o v e m e n t a s it s e e m s to o f f s e t th e S a l e s v i l l e fa u lt fr o m
i t s p r o j e c t e d c o n tin u a tio n - - t h e Sou th C o tto n w o o d C r e e k fa u lt. ■Su ch
m o v e m e n t in d ic a t e s th a t th e r a n g e fr o n t fa u lt i s y o u n g e r and e s s e n t i a l l y
u n in flu e n c e d b y th e w e s t - n o r t h w e s t t r e n d s .
V ^ o m e c o n t r o l fo r d a tin g m o v e m e n t on th e r a n g e fr o n t fa u lt e x i s t s in
th e SE ^ s e c . 21, T . 3 S. ,. R ; 5 E .
u n d is tu r b e d a lo n g th e fa u lt t r a c e .
T h e a llu v ia l fa n d e p o s it (Qf) is
L a te M io c e n e - - e a r l y P l io c e n e
f lu v ia t ile d e p o s it s (T . ), h o w e v e r , a r e d is t u r b e d a s th e y ab u t a g a in s t
P r e c a m b r ia n m e t a m o r p h ic r o c k .
fo r m a t io n o f th e a llu v ia l fa n .
T h u s m o v e m e n t h a d c e a s e d p r i o r to
82
Sub s u r f a c e F a u lt s of B a s in
G r a v ity and m a g n e t ic d a ta of D a v is and o t h e r s (1 9 6 5 ) s u g g e s t th a t
a " b e d r o c k tr o u g h " e x i s t s b e n e a th th e s o u th e a s t e r n m a r g in o f th e T h r e e
F o r k s b a s in .
T h e n o r th e r n b o u n d a r y o f t h is tr o u g h is f o r m e d b y a
b u r ie d fa u lt lo c a t e d s o u t h e a s t of G a lla tin G a tew a y ; th e s o u th e r n
b o u n d a r y i s fo r m e d b y a b u r ie d fa u lt t f en d in g r o u g h ly p a r a ll e l to the
G a lla tin R a n g e fr o n t fa u lt in th e m a p a r e a , b u t i s in p a r t c o in c id e n t w ith
th e la t t e r fa u lt to th e n o r t h e a s t ( s e e p la te I).
T h e s o u th e r n b o u n d a ry
fa u lt e x te n d s fr o m th e m o u th o f G a lla tin C a n y o n to th e m o u th of B e a r
C a n y o n (n o r th e a s t of th e m a p a r e a ) , a d is t a n c e of ab ou t 17 m i l e s .
D is p la c e m e n t on t h is fa u lt i s in e x c e s s of 4 0 0 0 f e e t b e n e a th South
C o tto n w o o d C r e e k , w ith th e f lo o r of th e tr o u g h (b o tto m o f b a s in f ill)
c o m p u te d to b e 6 0 0 0 f e e t b e lo w th e s u r f a c e (D a v is and o t h e r s ,
p . 3).
1965,
A s te p fa u lt r e la t io n s h ip m u s t t h e r e f o r e e x i s t b e t w e e n th e tr o u g h
an d th e G a lla tin R a n g e fr o n t.
T h e fa u lt on th e n o r t h w e s t s id e o f th e
tr o u g h e x te n d s n o r t h e a s t fr o m th e m o u th o f G a lla tin C a n y o n fo r m o r e
th a n 8 m i l e s , h a s a t l e a s t 2 0 0 0 f e e t of v e r t i c a l d is p la c e m e n t , and m a y
i n t e r s e c t th e s o u th e r n b o u n d a r y fa u lt n e a r th e m o u th o f G a lla tin C an yon .
N o r t h w e s t o f th e n o r t h e r n b o u n d a r y fa u lt th e b e d r o c k s u r f a c e r i s e s
g r a d u a lly to b e d r o c k o u tc r o p s in the C a m p C r e e k H i lls (D a v is and
o th ers,
1 9 6 5 , p , 3).
■ G E O M O R PH O L O G Y
D i s c u s s i o n o f th e g e o m o r p h ic h i s t o r y of th e m a p a r e a i s c o n fin e d to
tw o to p ic s :
in t e r p r e t a t io n o f th e g la c ia l f e a t u r e s and in t e r p r e t a t io n of
th e e r o s io n s u r f a c e s a t th e fr o n t o f th e G a lla tin R a n g e .
F o r a su m m ary
o f th e C e n o z o ic h i s t o r y o f th e G a lla tin R a n g e , the r e a d e r i s r e f e r r e d to
M c M a n n is (1 9 6 4 ),. M c M a n n is and C h a d w ic k (1964), an d H o r b e r g (1940).
G la c ia l G e o lo g y
B la c k w e ld e r (1915) n a m e d g la c ia l d e p o s it s in th e W ind R iv e r
M o u n ta in s o f W y o m in g th e B u ll L a k e and P in e d a le g la c ia t io n s ( e a r ly and.
la t e W is c o n s in r e s p e c t i v e l y ) . . T h e r e h a s b e e n a g r o w in g t e n d e n c y to
a tte m p t c o r r e la t io n o f W is c o n s in g la c ia l f e a t u r e s of th e R o c k y M o u n ta in s
w ith t h e s e tw o ,s ta g e s .
■E a r l y W is c o n s in G la c ia t io n
G la c ia l d e p o s it s t e n t a t iv e ly a s s ig n e d a B u ll L a k e a g e o c c u r a t th e
fr o n t o f th e r a n g e h ig h on an in t e r s t r e a m d iv id e b e t w e e n L it t l e B e a r
C r e e k and B ig B e a r C r e e k ( s e c . 5 , 6 , and 8 , T . 4 S. ,. R . B E . ,
31, an d 32, T . 3 S. ,. R . 5 E . ).
and s e c .
T h e d e p o s it s p r e d o m in a n tly c o n s is t of
s u b a n g u la r c o b b le s and b o u ld e r s o f M e a g h e r L im e s t o n e , P r e c a m b r ia n
g n e i s s , and P i l g r i m L im e s t o n e , w ith s a m p le s of o th e r f o r m a t io n s m a k in g
up a s m a ll p e r c e n t a g e of the. d e p o s it s .
T h e c o b b le s and b o u ld e r s e x p o s e d a t th e s u r fa c e a r e n o t d e e p ly
w e a th e r e d .
L im e s t o n e t y p e s a t d ep th in th e d e p o s it a r e o n ly s lig h t ly
w e a th e r e d , b u t th e m e t a m o r p h ic r o c k s a t d ep th a r e t y p ic a l ly d e e p ly
w e a th e r e d .
N o s t r ia t e d o r f a c e t e d r o c k s w e r e fou n d .
A p it dug in th e
84
g la c ia l d e p o s it o f T o m L a y P r a r i e r e v e a le d a n o t - t o o - w e l l d e v e lo p e d
s o i l p r o f ile .
T h e u p p e r p a r t o f th e B - h o r iz o n i s d o m in a n tly sa n d , but
a s.a m p le k n e e d e d w ith a s l i g h t a m o u n t o f w a te r te n d e d to m a in ta in a
b a ll, th u s in d ic a tin g th e p r e s e n c e of a s ig n if ic a n t a m o u n t o f c la y .
The
lo w e r p a r t o f th e B - h o r iz o n c o n ta in s p e d s ^ to jr in c h e s in d ia m e t e r ,
in d ic a tin g a g r e a t e r a m o u n t of c la y th a n in th e u p p er p a r t.
T h e s o il is
"w eak" but i s s t i l l b e t t e r d e v e lo p e d th a n th a t o f a P in e d a le d e p o s it
( p e r s o n a l c o m m u n ic a tio n ', J . M o n ta g n e , 1 966).
T h e a d v a n c e d s ta te
o f w e a th e r in g o f th e m e t a m o r p h ic r o c k s a l s o S u g g e s ts an a g e o ld e r th a n
P in e d a le .
A ls o th e a b u n d a n ce o f c o b b le s i z e lim e s t o n e r o c k s i s not
s u g g e s t iv e o f a p r e - B u l l L a k e a g e a s s u c h d e p o s it s a r e t y p ic a lly
c h a r a c t e r iz e d b y b o u ld e r s i z e lim e s t o n e t y p e s , if a n y l i m e s t o n e r e m a in s
a t a ll . A B u ll L a k e a g e fo r th e d e p o s it s e e m s to b e th e m o s t r e a s o n a b le .
A n in t e r e s t i n g and s ig n if ic a n t p r o b le m e x i s t s w ith r e s p e c t to th e
P a l e o z o i c lim e s t o n e p r e s e n t in th e d r ift. . It h a s no p o t e n t ia l s o u r c e a r e a
w ith in th e d r a in a g e s y s t e m a s th e s y s t e m p r e s e n t ly e x i s t s , w ith o u t
c r o s s i n g in te r s t r e a m d iv id e s or in c i s e d v a l l e y s .
A m a j o r d r a in a g e
c h a n g e s in c e P in e d a le g la c ia t io n i s u n lik e ly , a c o n c lu s io n s u g g e s t e d b y
th e f a c t th a t P in e d a le d e p o s it s o f th e M id d le C r e e k d r a in a g e (and r e g i o n ­
a lly ) a r e c o n fin e d to th e e x is t in g v a l l e y s .
H o w e v e r , it i s n o t im p o s s ib le
th a t c o n s id e r a b le dow n c u ttin g h a s o c c u r r e d s in c e B u ll L a k e t im e , and
th a t th e p r e s e n t ly d e e p ly in c i s e d c a n y o n s w e r e n o t y e t cu t.
T h u s, a
s o u r c e fo r th e l i m e s t o n e c o u ld p o s s i b l y h a v e e x is t e d in B u ll L a k e t im e
th a t w o p ld n ot r e q u ir e c r o s s in g an in c i s e d s t r e a m ca n y o n .
A p o s s ib le
s o u r c e a r e a fo r th e g la c ia l d e p o s it s b e in g c o n s id e r e d c o u ld th e n h a v e
85
b e e n in th e n o r t h e a s t c o r n e r of th e G a r n e t M ou n tain q u a d r a n g le .
O th er G la c ia l D e p o s it s
S m a ll g la c ia l d e p o s it s o c c u r at tw o lo c a t io n s in th e S ou th C o tto n w o o d
C r e e k d r a in a g e .
T h e y h a v e not b e e n a s s i g n e d an a g e b e c a u s e t h is w o u ld
r e q u ir e a k n o w le d g e of th e g la c ia l f e a t u r e s m u c h f a r t h e r up th e ca n y o n ,
an o b j e c t iv e n o t w ith in th e s c o p e o f t h is T h e s i s .
c h a r a c te r is tic s
H o w e v e r , th e p h y s ic a l
of th e d e p o s it s w ill b e n o te d h e r e fo r fu tu r e r e f e r e n c e .
In th e W j s e c . 7, T. 4' S. , R . 6 E . ,. c o b b le s and b o u ld e r s of
P r e c a p r b r ia n g n e is s o c c u r on a s t e e p s lo p e a t ab ou t 400 f e e t a b o v e th e
p r e s e n t s t r e a m l e v e l a n d a t an a v e r a g e e le v a t io n o f a b o u t 6 6 0 0 f e e t .
T h e r o c k s a r e su b r o u n d e d , a r e n o t s t r ia t e d , f a c e t e d , o r d e e p ly
w e a th e r e d , and a r e s e t in a p o o r ly d e v e lo p e d s o i l p r o f ile .
In th e SW ^ s e c . I,, T . 4 S. ,- R . S E . , su b r o u n d e d P a l e o z o i c lim e s to n e
c o b b le s a r e p r e s e n t on a s t e e p ly s lo p in g h i l l s i d e .
T h e d e p o s it s o c c u r
a p p r o x im a t e ly 600 f e e t a b o v e th e p r e s e n t s t r e a m l e v e l and a t an a v e r a g e
e le v a t io n o f about, 6800 f e e t .
T h e c o b b le s a r e su b r o u n d e d , an d a r e
n e it h e r s t r ia t e d n o r f a c e t e d , b u t th e y a r e d e e p ly w e a t h e r e d .
The
w e a th e r in g m a y b e due in p a r t to t h e ir p o s it io n on th e n o r t h e a s t slo p e
o f th e r id g e . . M o istu r e r e m a in s lo n g e r on s u c h s lo p e s and th e v e g e t a t io n
i s d e n s e , tw o f a c t o r s w h ic h p r o m o te w e a th e r in g .
E r o s io n S u r fa c e q
T h e g e o l o g ic m a p ( P la t e I) s h o w s a p p r o x im a t e ly w h a t a r e b e lie v e d
to b e th e d i s s e c t e d r e m n a n ts of th r e e m a j o r e r o s io n s u r f a c e s :
Q
g a nd Q g3 .
Q §p
T h e r e m n a n ts a s o u tlin e d s u g g e s t a g e n tle n o r t h e a s t
86
s lo p e of th e o r ig in a lly c o n tin u o u s s u r f a c e s .
O r ig in o f th e e r o s io n
s u r f a c e s i s in doubt e x c e p t th a t th e y w e r e p r o b a b ly cu t b y s t r e a m s
is s u in g fr o m th e G a lla tin R a n g e , a s s u g g e s t e d b y th e c l o s e c o r r e la t io n
o f s u r f i c i a l d e p o s it s (Q pa )-an d th e p r o b a b le s o u r c e a r e a s ..
N o r th w e s t o f
th e m a p a r e a , im m e d ia t e ly w e s t o f th e G a lla t in .R iv e r , M. D. M ifflin
(1963, U npub. !M .- S . T h e s i s , M on t. S ta te U n iv . , 1B o z e m a n ) fou n d a
s t e e p e n in g of th e ( n o r t h e a s t - s lo p in g ) e r o s i o n s u r f a c e s to w a r d th e
G a lla tin R iv e r C a n y o n ,
w ith .the o ld e r (h ig h e r ) e r o s io n s u r f a c e s in ­
c lin e d m o r e th a n th e lo w e r s u r f a c e s .
H e w a s n ot a b le to a s c e r t a i n
f o r c e r t a in th e c a u s e (o r c a u s e s ) of th e d if f e r in g d e g r e e s o f s lo p e .
M ifflin b e lie v e d , h o w e v e r , th a t th e e r o s io n s u r f a c e s r e p r e s e n t e d p e r io d s
of in c r e a s e d d is c h a r g e and d e t r it a l in c r e m e n t of th e G a lla tin R iv e r ,
d ir e c t ly r e la t e d to p e r i g l a c i a l c l im a t ic c o n d itio n s in th e d r a in a g e b a s in .
T h u s h e c o r r e la t e d e r o s io n s u r f a c e s ( t e r r a c e s ) w ith s t a d e s o f g la c ia t io n ,
h i s t e r r a c e N o . I w a s d e s ig n a t e d a s a P in e d a le f e a t u r e .
t h is d e c i s i o n w a s th a t " o u tw a sh d e p o s it s f r o m
T h e b a s is fo r
th e y o u n g e s t a lp in e
g la c ia t io n in th e S p a n ish P e a k s g r a d e d to a t e r r a c e w h ic h 1'a p p ea rs to b e
e q u iv a le n t to t e r r a c e N o . I' b e c a u s e o f i t s p o s it io n r e l a t i v e to
p resen t
r iv e r le v e l. "
T h e e r o s io n s u r f a c e s o f th e m a p a r e a m a y h a v e r e s u lt e d fr o m th e
sa m e phenom ena.
P r o o f o f t h is b y c o r r e la t io n of e r o s io n s u r f a c e s in
th e m a p a r e a w ith t h o s e o f M i f f l in s ' a r e a i s n o t f e a s i b l e , h o w e v e r ,
b e c a u s e : (I) th e r o c k t y p e s o f th e s u r f i c i a l d e p o s it s a r e d if f e r e n t .
In
th e m a p a r e a , th e s u r f i c i a l r o c k s a r e g r e a t e r th an 90% v o lc a n ic r o c k s ,
and a n y o th e r li t h o l o g ic t y p e s p r e s e n t r e f l e c t o n ly th e im m e d ia t e s o u r c e s
87
)
n e a r can yp n m o u th s (a t th e r a n g e fr o n t).
(2). C o r r e la t io n o f e r o s io n
s u r f a c e s in th e tw o m a p a r e a s on th e b a s i s of e le v a t io n i s r u le d out.
T h e e r o s io n s u r f a c e s o f th e w r i t e r s ' m a p a r e a a r e h ig h e r th a n t h o s e o f
M i f f l i n s ' a r e a , and a r e s e p a r a t e d f r o m t h e s e b y th e b r o a d G a lla tin R iv e r
v a l l e y b o tto m .
F a u lt in g a lo n g th e G a lla tim R a n g e fr o n t fa u lt (and p rob ab ly
th e b u r ie d tr o u g h f a u lt s a s w e ll) i s q u ite l i k e l y r e s p o n s ib le fo r s o m e of
th e e le v a t io n d if f e r e n c e s .
T h e r e f o r e , n o g la c ia l s t a d e - - e r o s i o n s u r f a c e
c o r r e la t io n i s p o s s i b l e .
N o r th w a r d t ilt in g o f th e G a lla tin V a lle y i s s u g g e s t e d b y (I) th e g e n tle
n o r th w a r d in c lin a t io n o f th e s u r f a c e s in th e m a p a r e a , and s t e e p s o u th ­
w e s t s lo p e s ; and ( 2) h e a d w a r d e r o s io n .p r o c e e d in g to w a r d th e s o u th w e s t
(m ig r a tin g up th e g e n t le s lo p e ) .
T h u s th e e r o s io n s u r f a c e in c lin a t io n s do
n o t r e p r e s e n t th e g r a d ie n t (o r g r a d ie n ts ) of th e s t r e a m w h ic h cu t th em ;
th e in c lin a t io n s a r e s t e e p e r n o w , an d a r e c e r t a in ly s t e e p e r th a n the
in c lin a t io n of th e p r e s e n t G a lla tin R iv e r flo o d p la in .
T h e s e d a ta s u g g e s t
th a t th e t ilt in g of th e e r o s io n s u r f a c e s m a y b e r e la t e d to r e c u r r e n t or
c o n tin u in g n o r t h e r ly t i l t o f th e G a lla tin V a lle y .
C O N C L U S IO N S
T h e fo llo w in g i s a l i s t of th e m a j o r c o n c lu s io n s d e r iv e d fr o m w o r k in
th e m a p a r e a .
(1)
T h e s e d im e n t a r y s e q u e n c e - is c o n s id e r a b ly th in n e r th a n e q u iv a le n t
s e q u e n c e ^ in a d ja c e n t a r e a s .
(2)
T r ilo b ite -s o f th e g e n u s 'G lo s s o p le u r a w e r e fou n d ip th e F la th e a d
Q u a rtzite; and a r e th e o n ly k n ow n o c c u r r e n c e of t r i l o b i t e s in th e f o r m a I
tio n . T h e y in d ic a t e th a t th e F la th e a d ^ if th e m a p a r e a i s y o u n g e r than
p r e v i o u s ly b e lie v e d ;
(3)
A c o n g lo m e r a t e s i m i l a r to th e S p h in x C o n g lo m e r a t e i s p r e s e n t
n e a r th e fr o n t of th e r a n g e .
(4)
T h e m a in d e f o r m a t io n o c c u r r e d d u r in g L a r a m id e t i m e , s ta r tin g
p r o b a b ly in th e L a te C r e t a c e o u s an d e f f e c t i v e l y p e a s in g b y th e t im e of
E o c e n e v o lc a n is m .
(5)
T h e s t r u c t u r a l m o v e m e n t s a r e n o t in c o n s is t e n t w ith an e a s t -
n o r t h e a s t c o m p r e s s iv e s t r e s s e v e n th o u g h th e tr e n d s o f s t r u c t u r e s a r e
n o t t h o s e e x p e c t a b le
t h e y w e r e fo r m e d e n t ir e ly b y su c h a s t r e s s
o r ie n ta tio n .
( 6) • S o m e s t r u c t u r a l t r e n d s of th e m a p a r e a e x i s t e d p r io r - t o
L a r am ide; d e fo r m a tio n .
(7)
A m p le e v id e n c e e x i s t s to p r o v e th a t th e G a lla tin R a n g e fr o n t
fa u lt d o e s e x i s t .
I
R E F E R E N C E S C IT E D
A lp h a,- A . G . , a n d 'F a n sh a w e ., J; R . , 19 5 4 , T e c t o n ic s of N o r th e r n B i g ­
h o rn B a s in A r e a and A d ja c e n t S o u t h - C e n t r a l M o n ta n a , in P r y o r
M o u n t a in s - - N o r t h e r n B ig h o r n B a s in , ..M ontana: B illin g lf -G e o l.
S o c . 5th A n n p a l F i e l d C on f. G u id eb o o k , p . 7 2 - 7 9 .
B a d g le y , P .. C . , 1965, ■S tr u c t u r a l and T e c t o n ic P r i n c ip le s :
R o w , N e w Y o r k , 521 p.
H a r p e r and
B la c k s t o n e , D . L . , J r . , ■ 19 5 6 , In tr o d u c tio n to th e T e c t o n ic s of the
R o c k y M o u n ta in s: 1956 G e o lo g ic a l R e c o r d , . R o c k y M tn. S e c . ,
A m e r . A s s o c . P e t r o l . G e o l.. (P u b . b y P e t r o le u m I n fo r m a tio n ,
D e n v e r ), p. 3 - 1 9 .
B la c k w e ld e r ,. E.“, 1915,. P o s t - C r e t a c e o u s H is t o r y of th e M o u n ta in s of
C e n tr a l W e s t e r n W y o m in g : J o u r . G e o l. , V . 2 3 , p . 97-117, 1 9 3 -2 1 7 ,
3 0 7 -3 4 0 .
B r o w n , C. W .,' 1959, H i a g e n e s i s of L a te C a m b r ia n O o lit ic L im e s t o n e ,
M a u r ic e F o r m a t io n , M o n ta n a and W yom in g: J o u r. S ed . P e t r o lo g y ,
v . 29, p. 2 6 0 - 2 6 6 .
C ob b an , W. A . , 19 4 5 , M a r in e J u r a s s i c F o r m a t io n s of S w e e t g r a s s A r c h ,
Montana": B u ll. A m e r . . A s s o c . P e t r b l. G e o l. , v . 2 9 , p. 1 2 6 2 -1 3 0 3 .
C o o p e r , G. A . , and o t h e r s , 19 4 2 , C o r r e la t io n of th e D e v o n ia n
. S e d im e n ta r y F o r m a t io n s o f N o r th A m e r ic a :- B u ll. G e o l.. S o c . A m e r .
v . 53 , p. 1 7 2 9 -1 7 9 4 .
C o o p e r , C . L . . a n d S l o s s , L . L . , 1 9 4 3 ,, C on o d a n t F a u n a and D is tr ib u tio n
of a L o w e r M i s s i s s i p p i a n B lp c k S h a le in M o n ta n a an d A lb e r ta : J o u r.
P a l e o n t ., v . 17,. p. 1 6 8 -1 7 6.
C r e s s m a n ,. E.- R . , and S w a n so n , - R . W. , 1 9 6 4 , S tr a tig r a p h y and
P e t r o lo g y of th e P e r m ia n R o c k s o f S o u th w e s te r n M on tan a: U. S.
G e o l.. S u r v e y P r o f . P a p e r 3 1 3 - C , 5 69 p.
D a v is , W. E . , K in o s h ita ,, W. T . , an d R o b in so n , G. D . , 1 9 6 5 , B o u g u e r
G r a v ity ,. A e r o m a g n e t ic , and G e n e r a liz e d G e o lo g ic M ap of the
• E a s t e r n P a r t o f the. T h r e e F o r k s B a s in , B r o a d w a t e r , M a d iso n ,
and G a lla tin C o u n tie s , M ontana: TL S. G e o l. S u r v e y G e o p h y s ic a l
I n v e s t ig a t io n s M ap G P - 4 9 8 .
90
D e i s s , C. , 19 3 6 , R e v is io n o f T y p e C a m b r ia n F o r m a t io n s and S e c t io n s
of M o n tan a a n d Y e llo w s t o n e N a tio n a l P a r k : B u ll. G e o l.- S o c .
. A m e r . , v . 4 7 , p. 1 2 5 7 -1 3 4 2 .
D o b b in , C. E . , a n d 'E r d m a n n ,, C . E . , 1 9 5 5 , S tr u c tu r e C o n to u r M ap
of th e M o n ta n a -P la in s : U. S. G e o !. S u r v e y O il and G a s I n v e s t i ­
g a tio n s M ap OM 178 B .
D o rf,- E . , and L o c h m a n , C. , 1940,, UppQr C a m b r ia n F o r m a t io n s in
S o u th e r n M ontana: B u ll. G e o l. S o c . A m e r . , v. 5 1 , p. 5 4 1 -5 5 6 .
D u tr o , J. T .,, J r . ,. S a n d o , W. J . , 19 6 3 , A g e of C e r ta in P o s t - M a d is o n
R o c k s in S o u th w e s te r n M o n ta n a a n d .W e s te r n W y o m in g , in G e o l.
- S u r v e y R e s e a r c h , 1963: U . S. G e o l. S u r v e y P r o f . P a p e r 4 7 5 - B ,
- p. B 9 3 - B 9 4 .
F e n n e m a n , -N. M . , 1 9 3 1 , P h y s io g r a p h y of W e s te r n U n ite d 'S ta te s :
Y o rk , M c G r a w -H ill B o o k C o. , In c. , 5 3 4 p.
N ew
F o o s e ,. R . M . , W i s e , .D . U . , an d G a r b a r in e , G. S. , 1 9 6 1 , S tr u c tu r a l
G e o lo g y of th e B e a r to d th M o u n ta in s, M on tan a and W yom in g: B u ll.
G e o l. S o c . A m e r . , v . 7 2 , p. 1 1 4 3 -1 1 7 ,2 .
. G u ts c h ic k , R . C . , and P e r r y , T . G . , 1959,- S a p p in g to n (K in d er h o o k ia n )
S p o n g e s and Their" E n v ir o n m e n t : , J o u r .. P a le o n t . , v . 33, p. 9 7 7 - 9 8 5 .
G w in n , V . E . , 1 9 6 1 , G e o lo g y o f th e D r u m m o n d A r e a , C e n t r a l- W e s t e r n
M on tan a: M on t. B u r . M in e s and G e o l. ,- S p e c ia l P u b . 21.
H a c k e tt, W. O. , an d o t h e r s , I 9 6 0 , G e o lo g y a n d G r o u n d w a ter R e s o u r c e s
o f th e G a lla tin V a lle y , G a lla tin C o u n t y ,, M ontana: U . S. Geol.,
- S u r v e y W a te r -S u p p ly P a p e r 1 4 8 2 , 2 8 2 p.
H a ll, W, B . , 19 6 0 , M u ltip le G la c ia tio n in th e M a d iso n and G a lla tin
R a n g e s , S o u th w e s te r n M o n ta n a , in -W e s t Y e llo w s t o n e - E a rth q u a k e
A r e a : B i l l i n g s G e o l. S o c . I Ith Annug.! F ie ld . C o n f. G u id eb o o k ,
p. 1 9 1 -1 9 9 .
H a ll, W., B . , 19 6 1 , G e o lo g y of P a r t o f th e U p p er G a lla tin V a lle y of
- S o u th w e s te r n M ontana: U npub. P h . D . T h e s is , U n iv . o f W yo. ,
239 p.
H a n so n , A . M . , 19 5 2 , C a m b r ia n -S tr a tig r a p h y in .S o u th w e ste r n M ontana:
M on tan a B u r e a u o f M in e s an d G e o lo g y M e m o ir N o . 3 3 , 4 6 p.
91
.H a n so n , A . M . , I 9 6 0 , C a m b r ia n o f th e M a d iso n R iv e r V a lle y A r e a ,
in W e st Y e llo w s t o n e - - E a r t h q u a k e A r e a : B il lin g s G e o l. S o c.
I l t h A n n u a l F iq ld C on f. G u id eb o o k , p. 2 0 7 -2 1 2 .
H o r b e r g , L . > 19 4 0 , G e o m o r p h ic P r o b le m s an d G la c ia l G e o lo g y of
th e Y e llo w s t o n e V a lle y , P a r k C o u n ty , M ontana: J o u r . G e o l. ,
V . 48 , p. 2 7 5 - 3 0 3 .
I m la y , R . W. ., 1 9 5 6 , M a r in e J u r a s s i c E x p o s e d in B ig h o r n B a s in ,
. P r y o r M o u n ta in s, and N o r th e r n B ig h o r n M o u n ta in s, W y o m in g
and M ontana: B u ll. A m e r. A s s o c . P e t r o l . G e o l ., v . 4 0 , p. 5 6 2 599.
I m la y ,, R . W. , G a r d n e r , L.- S. , R o g e r s , C . P . J r . , and H a d le y , H . '
D . , 1 9 4 8 , M a r in e J u r a s s i c F o r m a t io n s of M ontana: U . S. G e o l.
■ S u r v e y O il an d G a s In v . P r e l i m . C h a r t 32.
K a u ffm a n , M.- E . , 1 9 6 3 , G e o lo g y of th e G a r n e t- B e a r m o u t h A r e a ,
W e s te r n M on tan a: M on t. B u r , M in e s an d G e o l. , M e m . 39, 40 p.
K in g , P . B . , 1 9 5 9 , T h e E v o lu tio n of N o r th A m e r ic a :
J e r s e y , P r in c e t o n U n i v e r s it y P r e s s , 190 p.
P r in c e t o n , N ew
K le p p e r , M . R-., W e e k s , R . A . , and R u p p e l, E . T . , 1 9 5 7 , G e o lo g y
of th e S o u th e r n E lk h o r n M o u n ta in s, J e f f e r s o n and B r o a d w a te r
C o u n tie s , M ontana: U. S. G e o l. S u r v e y P r o f . P a p e r 2 9 2 , 82 p.
K u m m e I, B . , I 9 6 0 , T h e T r i a s s i c of S o u th w e s te r n M o n ta n a , im W e s t
Y e llo w s t o n e - - E a r t h q u a k e A r e a : B i l l i n g s G e o l. S o c . I Ith A n n u al
F i e l d C on f. G u id eb o o k , p. 2 3 3 - 2 3 8 .
L e b a u e r , L . R . , 1 9 6 4 , P e t r o lo g y of th e M id d le C a m b r ia n W o ls e y
S h a le o f S o u th w e s t e r n . M ont ana: J o u r . S ed . P e t . ; v . 34, p. 5 0 3 511.
L e b a u e r , L . R . , 1 9 6 5 , G e n e s is a n d 1E n v ir o n m e n t of D e p o s it io n of the
M e a g h e r , F o r m a t io n in S o u th w e s te r n M ontana: J o u r . S e d . P e t r o lo g y ,
v . 35, p. 4 2 8 - 4 4 7 .
L o c h m a n , C. , 1 9 5 0 , S ta tu s of D r y C r e e k S h a le of C e n tr a l M ontana:
B u ll. A m e r . A s s o c . P e t r o l . G e o l. , v . 3 4 , p. 2 2 0 0 - 2 2 2 2 .
L o c h m a n - B a lk , C. , 195 6, T h e C a m b r ia n o f th e R o c k y M o u n ta in s and
S o u th w e s t D e s e r t s o f th e U n ite d S t a t e s and A d jo in in g S o n o r a
P r o v i n c e , M e x ic o : I n te m a t . G e o l. C o n g . , 2 0 th , M e x ic o , p . 5 2 9 661.
9.2
L o c h m a n , C. , 1 9 5 7 ,. P a -I e o e c o lo g y of th e C a m b r ia n in .M o n ta n a and.
W yom in g: G e o l.. S o c . A m e r . M em . 6 7 , v . 2, p . 1 1 7 -1 6 2 .
L o w e ll, W. R . , and K le p p e r ,. M. R . , 1 9 5 3 , B e a v e r h e a d F o r m a t io n ,
. A L a r a m id e D e p o s it in B e a v e r h e a d C o u n ty , M on tan a: B u ll.
G e o l .- S o c . A m e r . , v . 64, p. 2 3 5 - 2 4 4 .
M c K e e , E . D . , and o t h e r s , 19 5 6 , P a l e o t e c t o n ic M ap s of th e J u r a s s i c
■ S y ste m : U . S . . G eoL - S u r v e y M is c . G e o l. I n v ., M a p .1 -1 7 5 .
M c M a n n is, W. J . , 19 5 5 , G e o lo g y of th e B r id g e r R a n g e , M ontana:
G e o l. Soc.- A m e r . ,. v . 6 6 , p. 1 3 8 5 -1 4 3 0 .
B u ll.
M c M a n n is, W. J. , 1 9 6 2 , D e v o n ia n S tr a tig r a p h y B e t w e e n T h r e e F o r k s ,
M on tan a, and Y e llo w s t o n e P a r k , in .T h r e e ■F o r k s - B e l t M o u n ta in s
A r e a an d S y m p o siu m : T h e D e v o n ia n S y s t e m of M o n ta n a and
A d ja c e n t A r e a s : B i l l i n g s . G e o l. S o c . 13th A n n u a l F i e l d C o n f.
G u id eb o o k , p. 4 - 1 2 .
M c M a n n is, W. J. , 1 9 6 3 , ;L a H o o d F o r m a t i o n - - A C o a r s e F a c i e s of th e
B e lt S e r i e s in .S o u t h w e s te r n M ontana: B u ll. G e o l. S tic. A m e r . ,
v . 7 4 , p. 4 0 7 - 4 3 6 .
M c M a n n is,- W.. J. , 1 9 6 4 , M a jo r D r a in a g e C h a n g e s in th e G a lla t in Y e llo w s to n e R iv e r 'R e g io n , M on tan a: - B il lin g s G e o l.- S o c . P a p e r s ,
M ay 1 9 6 4 , 9 p.
M c M a n n is, W. J . , 1965, R e s u m e o f-D e p o s it io n a l a n d -S tr u c tu r a l H is t o r y
of W e s te r n M on tan a: B u ll. A m e r . . A s s o c . P e t r o l. G e o l. , v .4 9 , p . 1 8 0 1 1823.
M c M a n n is, W. J. , and C h a d w ick ,. R . A . , 1 9 6 4 , G e o lo g y o f th e G a r n e t
M o u n ta in Q u a d r a n g le , G a lla tin C o u n ty , M ontana: M o n ta n a B u r e a u
of M in e s and G e o lo g y B u lle t in 4 3 , 47 p.
M id d le to n , G. V . , 1961,- E v a p o r it e S o lu tio n B r e c c i a s fr o m th e M i s s is s ip p ia n
of S o u th w e s t M on tan a: J o u r . S ed . P e t . , v . 31, p. 1 8 9 -1 9 5 .
M ifflin , M . D . , 19 6 3 , G e o lo g y of a P a r t o f th e S o u th e r n M a r g in of the
G a lla tin V a lle y , S o u th w e s t M ontana: U npub. M. - S. T h e s i s , M ont.
S ta te U n i v ., B o z e m a n , 111 p.
M o r itz , C. A . , 1 9 5 1 , T r i ^ s s i c and J u r a s s i c S tr a tig r a p h y o f S o u th w e s te r n
M on tan a:. B u ll.- A m e r . . A s s o c . P e t r o l . G e o l. , v . 35, p. 1 7 8 1 -1 8 1 4 .
/
.93
N o r d q u is t, J. W.
19 5 5 , P r e - R i e r d o n J u r a s s i c S tr a tig r a p h y in N o r th e r n
M on tan a and W illis t o n B a s in , in S w e e t g r a s s A r c h - - D is t u r b e d B e lt ,
M on tan a: B il lin g s G e o L - S o c . ~5th A n n u a l F i e ld C onL G u id eb o o k ,
p. 9 6 - 1 0 6 .
P e a l e , A . C. , 1 8 8 9 , R e p o r t of M r . . A . C . P e a l e to D ir e c t o r of U. S.
G eoL S u rv ey : U . S.. G eoL - S u r v e y N in th A nn u al R e p o r t, 1 8 8 7 -8 8 ,
pp. 1 1 1 -1 1 4 .
P e a l e , A . C. , 1 8 9 6 ,. D e s c r ip t io n o f th e T h r e e F o r k s Q u a d r a n g le , M ontana:
U. S. G eoL S u r v e y G eoL A t la s F o lio - N o . 2 4 , 5 p.
R e id ,. R . R . , 19 5 7 , B e d r o c k G e o lo g y of th e N o r th E n d o f th e T o b a c c o
R o o t M o u n ta in s , M a d is o n C o u n ty , M ontana: M o n tan a B u r . of
M in e s and G eoL M e m . 36, 25 p.
R e id , R . R . , 1 9 6 3 , M e ta m o r p h ic R d c k s o f th e N o r th e r n T o b a c c o R o o t
M o u n ta in s, M a d is o n C oun ty; M on tan a: B u l l . , G eoL ■S o c.- A m e r . ,
v . 74, . p. 2 9 3 -3 0 5 :
R ic h a r d s ,- P . W. ,. and N e is c h m id t , C . L . , 1957, T h e B ig H o rn
■ D olom ite in S o u th -C e n tr a l M on tan a and N o r t h w e s t e r n W y o m in g ,
in C r a z y M o u n ta in B a s in : B il lin g s G eo L S o c. 8th A n n u a l F ie ld
C onL G u id eb o o k , p. 5 4 - 62. ,
R o b e r t s ,. A.- E . , 1 9 6 1 , I n s o lu b le R e s id u e s and C a;M g-R a t io s in the
M a d iso n G ro u p , L iv in g s to n ,, M o n ta n a , in G e o L . S u r v e y R e s e a r c h :
U. S. G e o l. S u r v e y P r o L P a p e r 4 2 4 - B , p. B 2 9 4 - B 2 9 6 .
R o b e r t s , A.- E . , 1 9 6 4 , G e o lo g ic M ap of th e M y s t ic L a k e Q u a d ra n g le,
M ontana: U . S . G e o l.. S u r v e y , M is c e lla n e o u s G e o lo g ic I n v e s t i ­
g a t io n s , LJap 1 -3 9 8 .
. R o b e r t s , A . E . , 1965, C o r r e la t io n o f C r e t a c e o u s and L o w e r T e r t ia r y
. R o c k s n e a r L iv in g s t o n , M o n tan a, w ith t h o s e in o th e r a r e a s of
M on tan a and W y o m in g , in G eoL S u r v e y R e s e a r c h : U . S . G eoL
■S u r v e y P r o f . P a p e r 5 257TB,, p . B 5 4 - B 6 3 .
R o b in s o n , G. D . , 1 9 6 1 , O r ig in and D e v e lo p m e n t of th e T h r e e F o r k s
B a s in , M ontana: B u ll. G e o l. S o c . A m e r .-, v . 7 2 , p. 1 0 0 3 -1 0 1 4 .
R o b in s o n , G. D . , 1 9 6 3 , G e o lo g y o f th e T h r e e F o r k s Q u a d r a n g le ,
M ontana; U .. S. G e o l. S u r v e y P r o f . P a p e r 370,. 143 p.
R u p p el,- ip. T . , 19 5 0 , G e o lo g y of th e L im e s t o n e H i lls , B r o a d w a te r
C om ity, M on tan a: U . S. G e o l. S u r v e y , O pen F i l e R e p o r t, A u g u st,
'
19 5 O', 86 p.
94
S a n d b e r g , C. A . , 1 9 6 1 , W id e s p r e a d B e a r t o o t h B u tte F o r m a t io n of
E a r l y D e v o n ia n A g e in M o n ta n a and W y o m in g and i t s p a l e o ­
g r a p h ic s ig n if ic a n c e : B u ll. A m e r. A s s o c . P e t r o l. G e o l .,
v . 45, p. 1 3 0 1 -1 3 0 9 .
S a n d b e r g , C. A . , 1 9 6 2 , S t r a t ig r a p h ic S e c t io n of T y p e T h r e e F o r k s
and J e f f e r s o n 'F o r m a t io n s a t L o g a n ,. M o n ta n a , in T h r e e F o r k s B e l t M o u n ta in s A r e a and S y m p o siu m : T h e D e v o n ia n 'S y s t e m of
M on tan a a n d A d ja c e n t A r e a s : B i l l i n g s G e o l. S o c . 13th A n n u a l
F i e l d C on f. G u id eb o o k , p. 4 7 - 5 0 .
S a n d b e r g , C. A . ., 1 9 6 3 ,. D a r k S h a le U n it o f D e v o n ia n and M i s s is s ip p ia n
A g e in .N o r th e r n W y o m in g and S o u th e r n M o n ta n a , in G eo L S u r v e y
R e s e a r c h , 1963: U . S. G e o l. S u r v e y P r o f . P a p e r - ¥75 - C , p. C 17 C -20.
S a n d b e r g , C. A . , 1 9 6 5 ,. N o m e n c la t u r e and C o r r e la t io n o f L it h o lo g ic
S u b d iv is io n s o f th e J e f f e r s o n and T h r e e F o r k s F o r m a t io n s o f
' S o u th e r n -M o n ta n a and N o r th e r n W y o m in g : U.- S . G e o l.' S u r v e y
B u ll. 1 1 9 4 -N , 18 p.
S a n d b e r g , C.- A . , and H a m m o n d , C- R . , 19 5 8 , D e v o n ia n -S y s te m in
W illis t d n ,B a s in an d C en tra l M on tap a: B u ll. A m e r . A s s o c . P e t r o l.
G e o L ,.
42, p. 2 2 9 3 -2 3 3 4 .
S a n d b e r g , C . A . , an d M c M a n n is, W. J. , 1 9 6 4 , O c c u r r e n c e and
p a le o g e o g r a p h ic s ig n if ic a n c e o f th e M a y w o o d F o r m a t io n o f L a te
D e v o n ia n A g e in th e 1 G a lla tin .R a n g e , s o u th w e s t e r n M o n ta n a , in
G e o l. S u r v e y R e s e a r c h , 1964: U.- S. G e o l. S u r v e y P r o f . P a p e r
5 0 1 - C , p . C -5 0 -5 4 .
S a n d o , W. J. , an d D u tr o, J. T . , I 9 6 0 ,. S tr a tig r a p h y and C o r a l
Z o n a tio n of th e M a d iso n G rou p an d B r a z e r D o lo m it e in ,N o r t h ­
e a s t e r n U ta h , W e s t e r n W y o m in g , and S o u th w e s te r n M o n ta n a , in '
O v e r th r u s t B e l t of S o u th w e s te r n W y o m in g : W yo, G eoL - A s s o c .
15th A n n u a l F i e l d C on f. G u id eb o o k , p. 1 1 7 -1 2 6 .
S k e e ls , D . C. , 19 3 9 , S tr u c tu r a l G e o lo g y o f th e T r a il C r e e k - C a n y o n
•M o u n ta in 'A r e a : J o u r . G e o l. , v . 4 7 , p . 8 1 6 - 8 4 0 .
S l o s s , L . L . , 1 9 5 0 , P a l e o z o i c S e d im e n ta tio n in M o n ta n a A r e a : ■B u ll.
A m e r . A s s o c . P e t r o l . G e o l. , v . 3 4 ,. p . 4 2 3 - 4 5 1.
S l o s s , L . L . , and M o r it z , C . A . ,, 1 9 5 1, P a l e o z o i c S tr a tig r a p h y of
S o u th w e s te r n M on tan a: B u ll.. A m e r .. A s s o c . P e t r o l . G e o l. ,
v . 35 , p. 2 1 3 5 , 2 1 6 9 .
95
S m ith , J. G. , 1 9 6 5 , F u n d a m e n ta l T r a n s c u r r e n t F a u lt in g in, N o r th e r n
R o c k y M o u n ta in s: B u ll. A m e r . A s s o c . .P e t r o l. G e o l. , v . 4 9 ,
p. 1 3 9 8 -1 4 0 9-.
S o n n e b e r g ,, F . P . , 195 6 ,. T e c t o n ic P a t t e r n s of C e n tr a l M o n ta n a , in
C e n tr a l M on tan a: B il lin g s G e o l. S o c . 7th A n n u a l F i e l d C onf.
G u id eb o o k , p. 7 3 - 8 1 .
S p e n c e r , E . W. , and K ozak,- S. J. , 1 9 6 5 ,. T e c t o n ic S ty le in S p artish
P e a k s , M a d is o n R a n g e , M on tan a: W a sh in g to n and L e e U n iv e r s it y
G e o l. D ep t. R e p o r t N o. I, L e x in g to n , V ir g in ia , 5 3 p.
S w a n s o n ,. R . W. ,.._19 5 0 , G e o lo g y of a P a r t o f th e V ir g in ia . C ity and
E ld r id g e Q u a d r a n g le s , M on tan a: U .- S ., G e o l. S u r v e y O pen F i l e
R e p o r t, S p o k a n e,. W a sh in g to n , 1 2 ,p.
Tan's le y , W ., S c h a f e r , P . A . , and H a r t, L., H ., 19 33-,. A G e o lo g ic a l
R e c o n n a is s a n c e of th e T o b a c c o R o o t M o u n ta in s, M a d is o n C oun ty,
M ontana: M on tan a B u r , of M in e s and G e o l. M en a . 9 ,5 7 p.
W a lla c e , R . E . , G r ig g s , A.- B . , C a m p b e ll,, A . B . , and H o b b s, S. W .,
I9 6 0 ,. T e c t o n ic S e ttin g o f th e C o e u r d - A le n e D i s t r i c t , Id a h o , in
S h o r t P a p e r s in th e G e o lo g ic a l S c ie n c e s : U. S. G e o l. S u r v e y
P r o f . P a p e r 4 0 O-B,- p." B 2 5 - 2 7 .
W e b e r , W. M . , 19 6 5 , G e n e r a l G e o lo g y and G e o m o r p h q lo g y o f .the
M id d le C r e e k - A r e a , G a lla tin C o u n ty , M ontana: U n p u b lish e d M a s te r
of S c ie n c e T h e s i s , M o n ta n a ?S ta te U n iv e r s it y ,. B o z e m a n ,. M on tan a,
86 p.
W itk in d , I. J. , 1 9 6 4 , P r e lim i n a r y 'G e o lo g ic M ap of th e T e p e e C r e e k
Q u a d r a n g le , M o n ta n a -W y o m in g ; U.- S. G eo l.- S u r v e y M is c e lla n e o u s
G e o lo g ic I n v e s t ig a t io n s M ap 1 -4 1 7 .
soggooc
45*30
45*30
111 15
*
*
00'
'
GALLATIN COUNTY,.MONTANA
Rissell
G. Tysdal
presented to the faculty of the Department of Earth Sciences
RECENT A L L lj/IU M
T I Qo'
in partial fulfillment of H e requirements for the degree of
OJ
u
tr K
[o r
ALLUVIAL FAifi DEPOSIT
Z
[Qoa-J
OLDER ALLUMUM
Lu
I q » ..I
EROSION
SU? FACE
ii
IQq
i GLACIAL
DEPOSIT
<
O
6
N
O
Z
LU
r>
cr
3
O
>
cr
DEPOSIT
P 5 <
cr
GZ=I
VOLCANIC BRi CCIAS and FLOWS
o
UJ
—
E E = THERMOPOLIS
U
UJ
<D
C E O KOOTENAI
u
a
cr =5
3
I
UJ
Z
a)
O
Q
N
O
o
LlI
_l
Z
<
cr
CD
5
<
u
MORRISON
H O
SWIFT
ET
SHALE
FORMATION
F ) RMATION
FORM, TION
I Rl E RDON
FO
"D
*ATI ON
X)
%
>
D O
50y_
CV !GLOMERATE
G n a EOCENE?
a)
I
D O
SAWTOOTH
» ERMATION
E fO
QUADRANT
FORMATION
EmpZ ] AMSDEN
FOR vI ATI ON
H O
MISSION
CARTON
HO
LODGEPOLE
H O
THREE
O
JEFFERSON
O
RED LION
H O
PILGRIM
G O
PARK
G O
MEAGHER
GO
WOLSEY
LG O
G O
••••
V l l U t
Bozer .an, Montana
«Vi I
Vertical foliation
Strike and dip of flow banding
(igneous intrusive rocks)
Synclinal axis
Monoclinal axis
Contact
Fault
Reverse fault, showing dip
Subsurface fault, inferred from
gravity and magnetic data
Boundary of map area
A
9 0 0 0 -8 0 0 0 -7000
-=_z
6000
5000
FORMATION
Contour
Interval
40
Feet
B
B
I. MESTONE
FOI MATION
LIME STONE
8000-7000
£ P tr
_
SHALE
FLATHEAD
LIM :STONE
SHAf E
pJ
GNEISS
t
---------------------- -
S rsz.tj'. ------------- -
6000 - ■
5000
QUARTZITE
METAMORPHIC
A'
1966
LIMESTONE
I IMESTONE
FORK
Montana Vitate University
r - - 1? - < • I
I N , JSIVE ROCKS
LU
O In
U rj CO
<D
ll: <
S
FLUVIATILE
KiN cO uS
CT
-J
I
at
Strike and dip of beds
Overturned beds
Vertical beds
P POSIT
U j___ I
H
U
O
Tl
LANDSLIDE
«LL
r
O
foiri
X,
Maste- of Science
-------
II
pfg
- -
a
MONTANA STATE UNIVERSITY LIBRARIES
*