GEOLOGICGUIDE
TO
THE
TRAILS AT PHILMOI?T
SCOUT RANCH
Robert Balk
1953
GENERAL OUTLINE OF THE GEOLOGY AT PHILMONT RANCH
General Outline of the Geology at Philmont Ranch
N
o
t
e
: This outiine is written for the information
t o supervise geologic activities
of those who intend
of Scouts at the Ranch.
It i s not
for the use of individual Scouts.
The Ranch occupies about 200 square miles i n northwestern
New Mexico, located along the eastern slopes of the Cimarron Range,
which i s the name of the easternmost of the several north-south trending
ridges that southward continuetheFront
i s varied.
The eastern portion belongs
l e s s p l a i n s known as the Great Plains
e
Range of Colorado.
The scenery
t o the f l a t and relatively featurethat stgetch from Mexico north
beyond Alberta, accompanying the Rocky Mountains on the east.
p a r t of the Ranch property includes several steep, forested
The c e n t r a l
ridgesothat
rise appreciably above t h e l e v e l of the Great Plains. Their western
endings merge with the high, completely forested mountains
that make up the
western p a r t of the Ranch.
A view from Tooth-of-Time Ridge w i l l show that the vicinity
of Cimarron and the Philmont Ranch headquarters i s a r e l a t i v e l y low area,
surrounded on the north by the Raton Basin plateau, a great mass of
Cretaceous and early Tertiary shales and sandstones; and surrounded on
the south by several other, higher plateaus,
of the largest. Urraca
e
Mesa, seen Prom Headquarters, i s a smaller one.
These southern plateaus are
thesofter Cretaceous
of which Ortega Mesa is one
shales.
all capped by a flat basalt flow whieh overlies
The resistant sandstones 'of the Raton Basin
plateau axe, I believe,generallylacking
on thesouth.
-2-
Thelow
0
easterly portion of Philmont Ranch lacks the mesa-formand is, .instead,underlain
ing,resistantlayers,
Pierre shales,
They are well e&osed i n manylow
by the s o f t Cretaceous
h i l l slopes. hsevery-
strata slope at low angles
where i n t h e Rocky Mountain foothills, these
east or northeast.
Where the Ptterre
shales approach the axis of the Cimarron
Range, thghave been penetrated by many dikes of quartz-monzonite porphyry, and the presence of this very resistant rock has greatly influenced the scenery of the
middle portion of the Ranch area.
dikes trend north-south, dip vertically,
or at high angles t o t h e east.
They have given rise to several steep ridges.
that extends from north of Sawmill
The longest i s the one
Canyon southward t o the west end of
It is easily seen 'by the large gray cliffs
Tooth-of-Time Ridge.
e
i%
forms
along i t s entire cowse.
Tooth-of-Time Ridge is underlain, along
dike that strikes east-west, is aboutmilethick,
the entire east-west length
I do not know.
and extendsalong
PBdrre
Whether they show up at the north base,
Whether the Tooth-of-Time dike connects with some of the
meridionally trending dikes,
i s a l s o uncertain at present.
Neglecting the dikes,
ward-dippingCretaceous
we proceed'intothe
we should expect that from below the east-
shales older and older strata should emerge as
mountains.
Thisthey
the Front Range, there appears only
do.
erous age), before the crystalline rocks
However, i n t h i s p a r t
of
a r e l a t i v e l y t h i n sequence of red
shalysandstones and conglomerates(mostly,
reached.
i t s axis, by a porphyry
On the south flank, the
of the ridge.
shales d i p at about 40" south.
*
Some of the
it seems, of l a t e Carbonif-
of the core of the range are
And the combined e f f e c t of the purphyry dikes a d the generally
soft nature of these redbeds is t o conceal these old sedimentary rocks.
They are, however, f a i r l y w e l l exposed along the t r a i l up Cimarroncito.
I
~
Creek, and are seen f o r a few hundred f e e t along Rapdo Creek.
A s the
-3-
a
Cretaceous beds, the older sedimentary rocks dip eastward,
but more
steeply, 30-45".
that underlie the core
The crystalline, pre-Carboniferousrocks
of the Cimarron Range, consist of an oldest system.of:northeast-trending
amphibolites, or hornblende schists,
well layered, generally
fine-
or steep angles southeast.
grained rocks, dipping with intermediate
They
are intruded by thousands of lenticular, conformablbe masses of a pink or
reddish granite,
appropriate.
commonly so coarse-grained that the name, pegmatite, i s
Where l w g e numbers of these have enteredtheamphibolite,the
rocks display mixed characters, and the amphibolite
i s more feldspathic
of granite are, however, rare
thanelsewhere.Cross-cuttingdikes
it seems, restricted to short, thin dikes
and stringers.
and,
The most contin-
uous exposures of the pre-Carboniferous (very probably Precambrian rocks)
are along the
t r a i l from Abreu Base Camp t o and beyondRayado Camp (also
called Fi*Camp).
The a t t i t u d e s of the crystalline and later rocks are consistently at Variance, and there must be a profound angular unconformity be-
tween both rockgroups.
However, exposmes in the forested
t e r r i t o r y are relatively scarce,
and at the moment there i s no known expo-
sure of the unconformitynear any trail.
8oc. h e r . Bull., vol.
mountain
According t o Smith and Ray (Geol.
54, 1943),.who have done the only somewhat de-
tailed geological work i n t h i s p a r t of the range, the core
ron Range, including Bonito, Black, Bear,
tain, is a solid mass of crystalline rocks.
of the C i m a r -
Clear CreeE, and Tolby Moun-
However, it i s possible
that some of the highest and least accessible areas w i l l reveal later
sedimentary and volcanic rocks resting
e
on the crystalline basement.
Very generally, the history of the Cimarron Range is as follows:
Probably i n Precambrian time,
and certainly long before the Carbonifer-
ous period, a series of basaltic lava flows and ash or tuff deposits
were piled up i n a very thick series of layers.
They were subsequently
~
-4t i l t e d , but apparently not folded,
a
were brought t o levels of the crust
several miles below the then surface, and it was here that the system
of layers was mineralogically altered t o amphibolites, and penetrated
by very large volumes of granitic rocks.
Themore
gaseous fractions of
these crystallized as coarsequartz-feldspar-micaaggregates,the
called pegmatites.
as sandstones,lime-
Ordinarysedimentaryrocks,such
stones, or shales, must have been nearly absent
so-
i n t h i s s e r i e s of rocks.
A t l e a s t , their metamorphosed equivalents are conspicuously lacking.
I n Carboniferous and Permian time, this complex ofhetamorphosed
rocks has been a land mass, probably mountainous, and on both the west and
east sides large masses of coarse sandy debris accumulated.
A t l e a s t on the
west, there was a sea, and several thousand feet of sandstones and sandy
shales, with abundant marine fossils, a r e exposed on U.S. Highway 64,
e
between Taos and E a g l e Nest.
Interbedded with these marine
strata are
others that appear t o be swamp deposits f o r they contain many well
preserved f o s s i l plants, and some coal beds.
I n Cretacous time,
Pierre s h i e s are preserved many marine bivalves, cephalopods,
as marinedinosaurs.
of
a sea advanced, and.in the thick series
as well
Then the sea gradually withdrew, and fresh-water
sandssucceeded the shales.
They form the high plateau rim rocks north of
the Philmont Randh, and are the economically important
saxlistones of late
Cretaceous and Eocene age of the Raton coal Basin.
Some time after the deposition of the Eocene (early Tertiary)
sediments, the region
changed from one of deposition to one of u p - l i f t
and erssion. Exactly
when this p a r t of the Rocky Mountains has exper-
ienced i t s greatest uplift, and whether t h i s u p l i f t occurred once or
e
i n s e v e r a l stages, is not quite certain
at present.There
is reason t o
believe that perhaps i n Miocene time the quartz-monzonite porphyry
were intruded.
later than these.
They do cuttheCretaceoussedimentaryrocks,
Perhaps the aikes
60
dikes
they a r e
were intruded at about the time
Of
-5-
@
of g r e a t e s t u p l i f t of the range.
It i s probable t h a t some of the dikes
have served as feeders of lavaflows.
A l a r g ef l a t - w i n g
Thow of aph-
of Touch-me-not Mountain,
ahitic (dense) stony rhyolite crops out south
north of Cimarron Canyon, j u s t oubside the ranch area.
But whether it i s
connected with the great s i l l , o r dike, that forms the Palisades of the
Cimarron, has not yet been investigated.
Some time after the extbusion
of these siliceous lavas, the
canyon-Gutting of t h e C i m r o n Range began.
v e r a l stages.
It has developed i n se-
A t an e a r l y stage, possible Pliocene, the eastern slopes
seem t o have been f a i r l y smooth, connecting the high crest
of the
range with the f l a t f o o t h i l l s of t h e Rocky Mountains.Evidenceof
stage is found i n t h e widespread boulder-strewn
preserved both north
valleys have cut
smooth slope remnants
and south of Tooth-of-Time Ridge.
mir
profiles into,
andbelow,
this
The present
these older slopes.
A good example i s on the low mesa, about 1mile west-northwest of Head-
quarters.
The extensive basalt lava flows that cap Urraca, Ortega,
other mesas in the southern ranch
the large,
area, were probably extruded after
smooth slopes had been established.
Cretaceous shales,
&d
The basalt rests on
and judging from cursory observations I am inclined
t o assume there is a s l i g h t unconformity at the base of the flows.
Whe-
ther the lava also rests on gravels that had been accumulated on the
high-level slopes,
I do not know.Some
zontal, others dip gently
eastward, perhaps reflecting the general
gional slope of the Pliocene period.
e
of the Basalt mesas l i e h o r i -
re-
Rayado and othercreeksappear
t o have cut their present canyons several hundred f e e t below the levels
of these basalt flows.
There are no basalt flows that occupy canyens
or valleys of the present time.
There is no evidence that Ithis part Of the CiInarrOnRange has
-6-
a
Been glaciated during the Pleistocene period.
cirques, or roches moutonees.
There are no 'noraines,
WTRODUCTION
A
Geology at PhiLmont Trails
A rare opportunity i s waiting for you.
You have heard t h a t
Geology i s the science that deals with the features of the Earth.
haps you have already read your Geology Merit Badgebook,and
think that Geology I s an interesting Science.
Ranch, you canprove t o yourself that
On one side
you
While at PhilmontScout
i$ is8
You arrived at the Ranch, and looked around
geologistshould.
Per-
as every goo&
- which one? - , you notice flat, feature-
less plains,'and if you came from the East, you have been travelling
across some 1,000 miles of them,and
0
will rememberthem.You
are
fortu-
nate that you d i d not have t o cross these thousand miles i n a slow covered
wagon for you would have been held upby
thecare
for horses and the
constant search for drinking water. .But as you look west,
the plains are over.
you see that
You are face t o face with one of the. mostenormous
systems of mountains we have on the globe, the
Rocky Mountains.
One hund-
red years ago, men recognized that mountain ranges and t h e i r o r i g i n are
one of the large,fundamental
problems of the E a r t h .
After a century of
study, we are still far from a solution -ofthis problem; but we have
learned something.
We nowknow
that nearly all geological problems, and
certainly that of mountains, must be approached with patience, and by
close observation.
You had b e t t e r remember those two words.
If you do,
you may be the one who advances our knowledge and understanding of geo-
e
logy far beyond what we.nar know.
Now l e t uslook
at some of the details.
Ranch coversabout 200 squaremiles.This
The PhilmontScout
i s a minute fraction of the
area of the Rocky Mountains, but you are fortunate that within these
200 square miles
some very important and interesting features can be
-2seen,
Learn t o observe them, and go aboutyour work patiently, and when
yourtime
is up, you may have the greatsatisfaction
seen,begins
that w h a t you have
that you have begun t o understand something
t o make sense;
about the nature of the rocks around you; and that you have acquired a
feeling of w h a t a geologist has t o do i n the field.
Mountains and valleys, plains
and canyons do not happen,
are caused, l i k e thunderstorms or traffic accidents.
discover some of these causes.
them.
They
It is f o r you t o
Do not worry if you don% discover all of
Geology deals with big things,
and we human beings are
so small
i n comparison that we a r e lucky i f we succeed i n comprehending howsome
of the “biggest wheels” in
the geological laboratory work.
To do even
this weil, you have t o keep your eyes open, your mind alert, and notebook
and sharp pencil ready t o record w h a t you see, and w h a t you
w.
As you start your work, you learn that you can study very
fermt things.
Youmay
want t o study the large valley
Headquarters s t r a i g h t i n t o t h e
dif-
that leads fmm
mountains(Cimarroncitovalley)’.
Or you
may wish t o study she kinds of rock that underlie the slopes of t h i s and
neighboringvalleys.
You w i l l find much of interest there. Eventually,
you will w a n t t o extend your investigation
farther into the mountains,
t o see ehether mountains and plains are underlain by the saae types of
rocks or, if they differ, w h a t the relations are between the various
rockformations.
The plan of your geological work, while at Philmont,
i s very e l a s t i c .
It allows you t o spend somewhat more time on those items
that, i n you opinion, are particularly interesting,
If you are wise,
however, you w i l l not want t o leave t h i s area without having seen something of as many rocks, minerals, fossils,
i s t i c of this beautiful mountain land.
and outcrops as are character-
-3A good place t o start yourgeology work, i s the south-slope
the
"
,- h i l l
about
1"
mile
- west
1. e. massesof
t o see rock outcrops,
ders of pebbles.
is the color
of Headquarters.
ledges?.All,.solid,
Leave the Soad where ypu begin
rock i n place, not just loose boul-
Walk over theserocksslowly,
of the rocks?
of
and lookcarefully.
What
W
h
a
t i s the nature of the surfaces of t h e
massiverock?
Or doestherocktend
t o break up i n t o
thousands of l i t t l e chips? Is each chip a firm piece ofrock,
easy t o break t h e m down i n t o s t i l l smaller chips?
or is it
When you have made some
observations of this kind, s i t down, take a l i t t l e time, and write your
observations irhto yournotebook.
Write clearly, do notuse
or abbreviations. Three days later,
telesaph style,
you have forgotten the meaning of these
scribbled letters, and unless you have a photographic memory you cannot t r u s t
If you r e l y on your memory only you may as
your recollection of details.
0
well start anotherscience.
Yok geology will be unreliable, and the next
man who walks over your outcrops, will find yourstatementsincorrect.
Make it a r u l e never t o leave a group of rock ledges before
have written down a l l you .saw.
the United States..
you
There are nearly 3 million square miles in
There a r e l i t t l e more than 20,000 geologists and fewer
than 2,000 work i n t h e f i e l d .
To improve our knowledge of t h i s v a s t t e r r a i n ,
every geologist must l e a r n t o make r e l i a b l e ' a n d f a i r l y complete obseryations
at the places he saw.
If there i s time, walk on westward over t h i s h i l l slope.
You w i l l
have noticed by now that the most abundant rock shqm many newly horizontal
l i n e s on thesurface.
S&dy them.They
as i f a painter has drawn a numberof
m e important.
Are they mere lines,
streaks on the surface of the rock?
Or
would you say this whole mass of rock, as fax as you can examine it, is made
0
upof
layers?
-4This one i s an easy question.
You saw i n every l i t t l e g u l l y and
rill on that h i l l s~lopethatthestreakscontinueinto,
Therefore, every cubic.yard
it.
of t h a t r o c k must be composed of layers.
w i l l f i n d i n your Geology Merit Badgebookmuch
of l a y e r s i n rock.
andaround
You
information on t h e o r i g i n
Read t h i s i n t h e evening, not now, becauseyourtime
on
the h i l l is too precious.
Continueyourstudy
sils.
of t h e h i l l .
Perhaps this rock contains
They are remnants of animals or plants.
make a l l kinds of mistakes, picking
they are fossils. Generations
fos-
I n the beginning, you will
up odd-shaped bits of rock i n t h e b e l i e f
of geologists before you;have made the same
mistake, so donrt be discouraged i f some one with more experience says t o
you: "No, that one i s j u s t a form of weathering, or a peculiar crack i n t h e
rock."
e
Some day, yousll come through with a r e a l l y goodone,
know the difference. Perhaps-you'll find
hillside.
Then, a f t e r you spent.manyhours
know t h a t t h e r e a r e e i t h e r
and then you'll
no fossils a ~ a
t l l on t h i s e n t i r e
therelookingfor
none, or t h a t t h e y a r e p r e t t y
some, y o u * l l
hard to find. This
may be j u s t as important' a discovery as a. bag f u l l of fancy forms.
you are trying to learn the nature
curios.
Remember
of rocks; you are not a collector of
Whether you return with a collecting bag f u l l of mineral specimens
or f o s s i l s is unimportant, but that you leave this h i l l s i d e w i t h some c l e a r l y
written notes on w h a t you have seen there i s exceedingly important.
Let's go S t i l l f a r t h e r west on that h i l l .
towards t h e Animal Hospital, there
Where it slopes down
i s something unusual.
greenish knobs, about half way down theslope.Study
There axe a. few l i t t l e
.them carefully.
Are
the knobs arranged haphazardly on the h i l l , o r does there seem t o be some
system i n t h e i r l o c a t i o n ?
Examine therockitself.
t o , or dissimilar from the rock you studied before?
Ia it identical, similar
If it differs, observe
carefully i n which respect it differs, and write down'your observations after
youseem t o have seen nearly all the surfaces.
-5-
0
If you have a knife with you, see whether you can pry loose some of
theshiny
Lay a few of them at the t i p of
dark specks on therocksurface.
your finger, or a sheet of paper, and notice them carefully.
If you happen t o have a magnifying glass,
shape, their color, their size?
observe the grains through
What i s t h e i r
it.
Should you agree that all or most of these
grains are flat, like tiny sheets,
that they are of a brownish or a green-
ish color, that they measure about 1millimeter across,
t o be uniformly distributed through the rock,
and t h a t they seem
you have found about a l l you
can with the limit& equipment at hand, and have done a l l %hatany one can
do to describe these grains.
To gobeyond
it, and identify the substance
accurately, would require a petrographic microscope that i s operated with
polarized light and n i c o l prisms, as well as a s e t of ppecial3.y prepared o i l s .
With a l l t h i s , and tables prepared by mineralogists, checked and rechecked
over many years, an experienced mineralogist could
gra.ins of the mineral biotite before
a French mineralogist, Biot)
this mineral before,
colorless, flexible
sheets.
you.
t e l l you that you have
This i s the name (given i n honor of
No doubt, you have heard of
of a kind of mica.
and perhaps you have seen large sheets
of a nearly
mica, that could be peeled into thinner and thinner
You may also have heard that such mica sheets are commercia.lly
importantbecausetheyprovide
square foot in
good electrical insulation. Sheets, about
size, a r e used in generators of modern battleships.
our grains are much too small for such a use.
familiar geological problem:
.
1
Obviously,
You are now up against a
I
You have found a large amount of a commercially
important mineral, but i n your outcrop the mineral occurs i n such small grains
that it could not be mined at a p r o f i t .
0
Remember,we
have competition i n
t h i s world, and mica deposits much better than yours
have been discovered
i n many other p a r t s of the world.
-6Don.!% letthis discourage you.
.
You a r e out on this h i l l t o learn,
.
You have t o learn a thousand and one more things
not to start a mica quarry.
before you a r e ready t o start- a commercial enterprise.
ledges some more.
Bynow,
you have probablynoticed
i n one direction.
mica-richrockextenddominantly
you write that into yournotebook.
So l e t us study the
that the ledges
Which i s i t ? Be sure
Next, t r y t o figure out the
rock body t o which these mica-rich ledges belong.
of the
shape of the
You realize, of course,
that some of the rock may have been removed by rainwash and wind before you
arrived there,
mass.
so t h a t you should t r y t o r e c o n s t r u c t t h e
Would you say, the dark
ball, a &late,
of a
micaceous rock has the approximateshape
a cube, a systemof
ever your conclusion,,'write
shape of t h i s rock
roots, a row of lenses, a matchbox? What-
for
it down, and write alongside your reasons
calling it the oneand not the others.
e
Now, noteanotherverycuriousfeature.
grayish-brownrock
Where thesurrounding
t W t makes up most of t h i s h i l l s i d e approachesthe
micaceous
rock, it changes within a few f e e t i n t o a nearly black, splintery, very
and tough rock,
both came from one and t h e same formation.
do, as.you can check i n many places.
Yet they
Be sure you write down a l l these
you make them. Don't take anything i n
granted.Trustneither
wrong.
hard
so different from the ordinary one that you would not know
t h a t loose specimensof
observations as
dark
this folder for
your memory nor anyone e l s e ' s words.
They may be all
You alone can make those observations that you can r e l y on.
If you and I made about the same observakions, we may agree 'chat
the micaceous rock has had some peculiar effect on the surrounding grayishbrown rock.
If you look carefully,
you w i l l recognize that the layers of the
surrounding rock that chips so easily, remain visible in the darker,
haxd rock.
The layers go r i g h t up t o t h e boundary with the micaceous rock, and arc then
cut
off.
If you saw t h i s , and perhaps noticed
also how the layers of the
-7surrounding rocks havebeen t i l t e d and deformed.at one of the easternmost
0
exposures of the dark micaceous rock, you have madesome
very important obser-
vations,,provided you wrote them a l l down i n your notebook in clear, readable.
form.
If you want t o do something extra, s i t down i n f r o n t of oneof
interesting leeges,
the most
and sketch with your pencil what you see before you.
Nobody
expects you t o be a a a r t i s t , but i f you want t o be a geologist, you must learn
t o draw, perhaps crudely, w h a t your eyes have seen.
It i s astonishing howmuch
most of us overlook i f we never sketch rock outcrops
i n nature.
your sketch,
When you f i n i s h
mask i n the upper l e f t - and right-hand corners the appropriate
geographic directions.
If you look straight to the south,
l e f t and west on your right.
If you face northeast,
you have east onyour
you have northwest onyour
l e f t , and southeast on yo& right, and .so forth.
If you are s t i l l around t h i s ledge, have written down all your
observations, and perhaps made your f i r s t geological sketch, you deserve a
l i t t l e reward, because t o complete all t h i s w i l l have taken you well over an
hour, and your feet may ache.
they got there,
You now want t o know w h a t these rocks mean,how
and w h a t you can l e a r n from them.
Two hundred years ago, nobody
would have t o l d you anything about such hillsides,
u t t e r l y perplexedaboutthecuriousnature
andyou might have l e f t them
of rocks.
Nowadays, you have at
your disposal the accumulated experience of many generations of geologists, made
easily accessible in textbooks
and special reports.
A few geologists
have walked over the h i l l you stand on, and the surrounding t e r r a i n .
Thanks t o t h e i r s t u d i e s ,
you can learn that the
main rock on t h i s h i l l
i s a shale, was formed during the so-called Cretaceous period
earth’s history and, as you should verify, the layers
l i e exactly horizontally, but slope
downward to the northeast.
of t h i s shale do not
(or, as we ia geology, dip) gently
The dark, micaceous rock is a volcanic rock, i n
f a c t a very rare type as volcanicrocks
minette, and in addition to the dark
amount of potash feldspar,
of t h e
go.
It has t h es c i e n t i f i c
name,
mica, b i o t i t e , it contains a large
and traces of several other rarer minerals.
If
you observed, as you havebeenasked,
0
what the shape of t h i s rock is, you
w i l l agree that it could be called a tabular rock body, perhaps 6 f e e t
wide, and exposed for aboutfeet
in
a
direction.
b e t t e r f i l l out these two blankspacesbefore
You had
you leave the hill.
Estim-
ating distances i s something all Scouts and Geologists must be able t o do.
Also, look up your Geology Merit Badgebook t o f i n d a special name by which
geologists refer t o tabular volcanic
(or igneous, i n re5erence t o t h e L a t i n
word f o r fire, ignis) rocks that penethate the rock layers
Younuw
have quite a collection of questions you will want.to
read up on at home.
(I) What i s a shale? (2) Eow is it formed? (3) Is
the Cretaceous period relatively late
(4) Roughly, howmany
theEarth?
t o have lasted?
e
of the earth's crest.
or e a r l y when we consider the age
of
years i s theCretaceousperiodbelieved
(6) Can you t e l l something aboutthe age of the minette?
you must think twice before you are ready with an answer here.
On one thing, yourbookletdoesnotsupplytheinformation.
does not t e l l ' you why the Cretaceous shaie,
turns into a dark, splintery rock.Well,
all the information
as it approaches the minette,
an &-page bookletcannotprovide
you need i n a particular area..
many non-igneous rocks have been a l t e r e d i n someway
contact with volcanic rocks. In 'chis particular
Experience has shown t h a t
where .they have come i n
example, the effect happens
t o be very similar t o w h a t we do a r t i f i c i a l l y when we make bricks.
making, you start out with clay
It
For brick-
(and as you will find i n your booklet, clay
and shale have t h e same composition; t h e main difference is that shale has been
compressed t o some extent), you shape the soft clay,
and push t h e s o f t b r i c k s
i n rows i n t o a brick-oven, where you heat them t o temperatures of over
Fahrenheit.
0
The clay substance,
develop crystals,
pretty hard rock.
l,OOOo
exposed t o this heat for many hours,will then
and most of them are hard. Therefore, the
fired brick is a
The Cretaceous shale has been baked i n t o something l i k e a
natural brick in contact with the minette. This particular
dark minerals, so small you can not
rock, composed of
identify them with the naked eye, -and com-
-9monly of a brownish, or dark gray color, has been called, hornfels
(meaning "horn-like rock" in German). The term is used internationally
for
this
typeof rock and a rock so altered
by
igneous
heat
is
called
"contact;
metamorphosed". You can say: "The hornfels is a contact-metamorphosed
Cretaceous shale", or "The splintered rock ais
Cretaceous hornfels".
You
willhave more questionsas you leave this hill. You wonder,
of course, %hether this mass
of minette belonged to
a former volcano. If
there was one, bas
it disapperaed before our time. Perhaps there nowas
volcano. You caxi not get the answer at this hill& But keep the question
alive in your mind. Somewhere else, at some other opportunity,
an answer
also are wondering why the hillside is
may present itself. You probably
strewn
withso many large boulders of rocks unlike the Cretaceous shale. Again,
the answer is not at hand.
You-cansee, therefore, whyyou should be patient
the answer to all
our questions,
in geology. If every hill us
gave
geology would, indeed, be
an easy science. But don't despair. We
will
come
across
more
boulders
elsewhere.
TRIP TO CIMARRONCITO CAMP,
AND
WESTWARD TOWARDS LAMBERT
AND CYPBER1S MINES
n
T r i p t o Cimarroncito Camp, and Westward towards Lambert and Dypherts Mines
On your exploration at the hill, 1mile west of Headquarters
shale that
you became acquainted w i t h the brownish-gray Cretaceous
flakes e a s i l y i n t o l i t t l e soft chips.
into the mountains t o the west.
Today,you
w i l l proceed farther
You w i l l drive along the
and, as you pass the ledges, they should look familiar to
Same road
you, and you
should have no GTifficulty recognizing the minette outcrops near the
west endof
the hill.
Westward, f o r about 5 miles, the road follows the broad,
of Cimarroncito Creek and does not pass
flat-bottomed valley
spicuousrockoutcrops.
make observations.
i n t h i s camp.You
While driving through this area, continue to
Remember, you are spendingonly
a few days o r weeks
have very much t o observe and record if you want t o
leave with a reasonably complete idea. of the geology.
you can see smooth, grassy slopes,
times they are f a i r l y c l o s e ,
From the car,
of the same grayish colors as the
h i l l with the minette ledges, to the north
featureless slopes,
many con-
and south of the road.
sometimes over a mile away.
A l l of these
if youhad the time to walk over them,would
be underlain by the same flaky brown or grayish shales.
Some-
prove t o
As you wonst
have the time t o map every square mile of t h e Ranch during your stay,
you
may as well be told that the shales underlie most of the foothills leading
to the forested slopes farther west. Shales
are, in fact,
of theCretaceousperiod
one of the most widespread types of rock anywhere between'
Mexico and Alberta.
This particular shale formation was f i r s t described
i n South Dakota, about 90 years ago.
it i s called the Pierre
shale.
I n reference t o a localitythere,
You w i l l find. this name printed on your
Ranch map ( i n pocket of your brown Program Hand Book).
Thename
stands
-2f o r a large area underlain
by the Pierre shale.
Twenty years from now,
we shall probably have a much b e t t e r map i n which the exact limits of
this formation have been drawn.
But when it comes t o geological exploration,
New Mexico i s s t i l l pioneer country,
and our knowledge of the distribution
Some of your future
i s notveryaccurate.
of thevariousformations
observations, i f they are reliable, will help us extend our knowledge.
From these remarks, it should be clear t o you as you look
across the valley
t o the south, that the steep crags
Of-Time Ridge, a r e probably of a different rock,
r e s i s t weatheringprocesses
geologist, travelling in
suchdifferences
- one that seems t o
shale.
much better than the soft Pierre
new terrain, shouldalwayskeep
i n r e l i e f forms.
areas, the difference
that make up Tooth-
his eyes open for
Here the contrast i s extreme,
i s more subtle,yetrecognizable.
A
I n other
Many a productive
o i l and gas f i e l d has been discovered by geologists who Eept t h e i r
@ ~ p
open t o the meaning of these s l i g h t c o n t r a s t s i n t w i n and r e l i e f features.
Where the road passes c l o s e t o Webster Lake, you see shale
exposures near the
road, and on your right (north), forward,
the large flat-topped hill, called
word for table.
Deer LakeMesa.Mesa
you can see
i s t h e Spanish
You can see wby the word i s appropriate.Nearly
mesas owe t h e i r flat top t o a particular kind
Mountain region, there
of rock.
all
I n t h e Rocky
are scores of mesas, small ones and large ones.
Perhaps you have heard, or read,
The l a r g e s t ones you can call plateaus.
something on how pilateaus &e formed.
It has something t o do with a
flat, r e s i s t a n t plate of rock, and erosion.
time later you w i l l have a chance of
Keep t h i s i n mind.
Some
studying t h i s m a t t e r i n more &Tail.
As you proceed, the surface rises,
and t h e road becomes rough;
f i n a l l y , you pass a large, t a l l gray c l i f f t o t h e
i s a beautiful reservoir with drinking water
north.
I n f r o n t of it
for t h e town of Cimwron.
A t this c l i f f , you have l e f t behind t h e g e n t l y r o l l i n g h i l l s
and plains
of the Rocky Mountain f o o t h i l l s , and you are now i n very different terrain,
-3mountainous, forested, more complicated,but
you leave the car
0
more interesting.
at theCimarroncito Base Camp.
Soon
Gather up yournotebook,
t o it that your pencil i s sharp, and that
hammer, magnifying lens, see
you have a k n i f e t o sharpen it from time t o time.
We follow the t r a i l that leads westward from Cimarroncito Base
Camp along Midale Fork
of Cimarroncito Creek.
Directly as you start out, you will notice yellowish-gray
gravel on the trail.
Don't stop now, but remember it. Thirty feet
beyong t h e barbed wire gate, on your right (north), there
crop of rock.Stop,
you see.
'
and examine it, and be sure you write down w h a t
You should know t h i s rock a s an old friend now.
amined therocks
i s an out-
If you ex-
l m i l e west of Headquarters, you should
at t h e h i l l ,
know very soon t h a t t h i s outcrop, even though
it i s small, i s the same
Cretaceous Pierre shale.
0
This i s a very important discovery,
t o associate the dark Pierre
So f a r , you.have learned
open country.
shales with flat,
Now you have passed across high, steep cliffs,
here you find the
the steep cliffs
ing.
and it should puzzle you.
same s o f t shale.
Thisdoesnot
make sense.Obviously,
must be composed of a different rock, r e s i s t a n t t o weather-
The s o f t shale cannotgive
stay in the car until
ately, you can makeup
rise t o v e r t i c a l crags.
As you had t o
you arrived at th.e Cimarroncito Base Camp, you could
not examine the rock in the
k g e c l i f f n o r t h of the reservoir. FortunWalk on 100 feet, and j u s t as you come
for this.
t o t h e creek, you find on your north side a ledge.
and go t o workon
and yet
this rock.
It is worth it.
Take outyour hammer,
The ledge i s notlarge,
and the blocks axe hard t o g e t ' o f f , b u t you must get hold of a reasonably
0
large piece,
and then obtain
a
'2
fresh surface.
at once see why t h i s is important.
most rocks look quite different
If you get one, you will
The ordinaryweatheredsurfaces
from the fre& rock
inside.
of
yo recog-
-4-
nize a rock, and t o s p o t i t s constituents, you must examine fresh surfaces.
By the creek,
you w i l l find many loose, clean blocks.
the same as the rock in
you ledge.
Theyseem
t o be
But as you are concerned with the
rock of t h i s one ledge, you had better forget these nice, clean blocks
for the time being, and concertrate on that dark, inconveniently located
ledge
If you have great (Eiffuculty getting your specimen here, walk
There i s anotherledge
some 100 f e e t beyon6 the ford.
of t h e trail.
Specimens from either ledge are
on the south
side
good for yourpurpose.
If you laok at a fresh, clean, dry surface
of t h i s rock, you
w i l l at once recognize dozens of white or yellowish grains, squarish
i n shape.
%eymake
up more thanone-half
face in the sunlight,
e
reflect the light
Turn the sur-
and you w i l l recognize that the light-colorea grains
from smooth internal planes.
and examine them withcare,
If you have a hand lens,
you will spot some grains that r e f l e c t from
two s e t s of such smooth planes.
minuteedges.
of t h i s rock.
Where they intersect, they
show s t r a i g h t
If you were a chemist, you couldanalyzethesegrains.
would find they a l l a r e composed of silica (Si02),
(CaO), soda ( N q O ) , and potash (QO).
You
alumina (A12O3), Lime
Substances that have an identifiable
chemical compos%tion, a characteristic structure and build up rocks, are
called minerals. This particular mineral,
and the two systems ofplanes
with this chemicalcomposition,
t h a t are smooth (and other characteristics
which you l e a r n i n a course i n mineralogy), is called feldspar.
very important and widespread mineral.
The property of a mineral t o s p l i t
along s e t s of smooth internal planes, is called cleavage,
*
feldspar has 2 good cleavagesystems,Actually,
cleavage, but the planes
l i k e l yt o
It i s a
and we say that
feldspar.has a t h i r d
of t h a t s e t do not s p l i t e a s i l y , so you are not
spot them.
What else do you see on fresh surfaces of you new rock? There
are dark grains, smaller than the feldspars, nearly black, usually
a dark
-5that you find a few good ones.
green.See
some have t h e shapeof
f l a t plates.
rock.
YOU 6.0,
or needles,
short sticks,
With your k n i f e , t r y t o p r y
do not come off easily,
If they are large enough, t r y your
but some .of' the flat, shiny grains do.
You w i l l then recognize a mineral familiar from
magnifying glass onthem.
The flexible sheets are b i o t i t e mica, t h e
the trip to the minette ledges.
The other dark mineral, in slender prisms and
needles, lacks the perfect cleavage
muchmore
whereas others are like
some of these dask grains off the
you will find that the slender dark needles
same as i n the minette.
you will notice that
that some of them have a shape
If you a r e lucky, you'll see
like a hexagon.
If
As you can not t e l l
of the biotite.
about it without a microscope, you may as well know that t h i s
mineral i s calledhornblende,
or amphibole. 'This is, i n f a c t , t h e
of a large group of minemls.
name
They have a wide d i s t r i b u t i o n i n t h e e a r t h t s
Your kind of hornblende i s dark on account of iron oxide, which is
crust.
combined 'in the mineral with silica,
manganese oxide.
alumina,lime,
magnesia, and some
Amphibole entir&y free from iron oxide 5s colorless.
You find it i n c e r t a i n marbles.
But most amphiboles are greenish,
even
black.
There i s s t i l l anothermineral
large grains.
pebbles.
If they broke out
i s quartz,probablythe
the crust of the earth.
and it
will scratch your s t e e l knife.
amountof
.
so hard.
B u t if a minute
it win at Once
brown, nearly every color
Remember, therefore, that the color
in
it lacks cleayage,
Few other minerals are
it has no color of i t s own.
-yellow, red,black,
inside, l i k e
most abundantmineral
a mineral pigment i s present in quartz crystals,
Color the quartz,
forms
l i k e gxay or pinkish
You can easily identify quartz;
Quartz is l i k e g l a s s i n t h a t
found.
whole, theylook
If you broke them through,theyarecolorless
Thismineral
glass.
i n your rock.I$,too,
has been
of quartz i s notdiagnostic,
nor i t s accidental shage; but i s hardness, glass-like greasy luster,
lack of cleavage are good c r i t e r i a i n determining the mineral.
and
-6-
e
Why the quartz grains in this
unknown.
rock should look
l i k e pebbles i s
It is an uncommon feature as i s the opaque, whitish shell of
the grains.
You w i l l f i n d that the amount of quarte in this rock varies
from one ledge t o another.
i s the very fine-grained
The last portion of the rock you must note,
groundmass, of dark gray color.
I have not seen
it under the microscope, and do not know w h a t minerals it may contain.
Perhaps i n another year, the rock
will have been examined microscopically.
Even so, you can see that t h i s rock i s t o t a l l y d i f f e r e n t from
the Pierre shale.
It consists of a great many crystal grains (the
crystal, and mineral, could
be used interchangeably; some persons prefer
the first word if the grain i s terminated by straight faces.
aboutotherconnotations
words,
of these 2 words).
s i z e f o r you t o recognize them.
Don'tworry
They are, 'however, of s u f f i c i e n t
And between them i s a groundmass, or
matrix, of microscopically small grains.
Thetwo
ledges of t h i s rock do not allow you t o estimate the
shape of the rock.
you.
But you see that it builds up t a l l c l i f f s around
It extends generally across the valley
Creek, and you do not see
any layering.
of Middle ForkCimarroncito
Two hundred years a.go, a very
famous leader i n geoh3gywould have pronounced t h i s rock an ocean deposit, like
sand o r mud.
He did not know that crystals of feldspar,
amphibole, and b i o t i t e r e q u i r e temperatures of about l,OOOo Fahrenheit
t o form; and it has been established
that many volcanic rocks which congeal
i n suspension.
before our eyes from molten lava, carry such crystal grains
The frozen rock displays thousands
grained groundmass.
rock.
of nicely formed c r y s t a l s i n a fine-
O u r rock, in short,
i s anothervolcanic,
Quite different i n appearance from theminette.
or igneous
Again, there i s
no xolcano overhead, and again you can not t e l l where at the surface of
the earth thislavaerupted.
The rock is completelycold
wonder how long ago t h i s l a v a flowedthroughtherocks.
answers m y questions i n one place. There are
now, and you
Nature r a r e l y
more rockoutcrops
t o come,
-7so
keep aneye on those problems f o r which,you lack an answer.
as you do not yet knowhow
to.examine a rock microscopically and deterrbine
t h e s c i e n t i f i c names of igneous rocks,
Theword,
t h a t this rock i s i n
you mayknow
It i s called a "quartz-monzonite
composition somewhat similar t o granite.
porphyry".
However,
porphyry, means that the rock
i s composed of large,
well formed crystal grains embedded i n a much finer-grained groundmass.
Theword,
monzonite, r e f e r s t o Monzoni, a v i l l a g e i n t h e I t a l i a n
where such a rock was first described by geologists.
Geology i n l a t e r y e a r s ,
Alps,
If you go on with
come t o a good library, and can boast of a. smat-
tering of German, you may enjoy the first chapter i n Waldemar Christian
Broegger's "Die Eruptivgesteine des Dristianiagebietes, Vol. 2: Die ErupI1
tionsfolge der triadischen Eruptivgesteine bei Predazzo i n Sudtirol",
Videnskabs-Selskabets Skrifter, I.
Mathematisk-maturv.
Klasse, No. 7,
1895. It i s a c l a s s i c , l i k e Darwints "Origin of Species", o r G. K. G i l b e r t ' s "Geology of the Henry Mountains, Utah".
Fiegian geologist,Broegger, looks through the 'guest
"The Golden Ship", at Predazzo,near
..
I n thischapter,the
bookof
Eor-
the Hotel
Monzoni, and r e c a l l s t h e achievements
of the scores of famous geologists who registered there while making
geological observations
on the huge c l i f f walls near Monzoni.They
were
concerned with problems that a r e s t i l l among t h e most fundamental i n
physical geology.
But you need not waste time w i t h t h i s now;
instead,
you had better continue your observations.
One thing you have not been able
crops:theshape
of theigneousrock.
climb up on t h e c l i f f s t o t h e n o r t h
t o discover at the last out-
If you had ample time, you might
and south of the ravine,
and per-
haps you could see the general shape of t h e monzoniteporphyry.
But
the pines grow so t h i c k l y t h a t you can not see enough from the bottom of
theravine.
Be patientagain,
t h e shape of the igneous rock
and remember t h a t you w a n t t o findout
what
i s when the opportunity comes.
The c l i f f of monzonite porphyry
soon withdraws from the trail,
-8and you see no rocks for about
a
look at some of the boulders that l i e by t h e trail.
various kinds.
you a chance t o
1,000 feet. This gives
They are loose, and of
Break a few with a hammer, t o obtain fresh surfaces,
a note in yournotebook
comparethem with rocks you already know.Make
what kinds of rock you think you recognize.
them also, write
and
If you see others, examine
down w h a t you can see, and again be patient.
If the
boulders l i e around i n t h e bottom of this ravine, quite probably there
w i l l be ledges of them where you can examine them at your leisure.
And
should you be unable t o follow this particular valley far enough t o come
t o them, there i s a chanceof finding them i n some other trail.
As you pass through the next
t h e bottom of the small creek.
few hundred f e e t , you may obserqe
It i s covered i n most places with boulders.
Why should t h i s be so? You will see so many while you a r e at Philmont, and
they are discussed i n your Merit Badge booklet that you do not need any
special
information
on t h i s .
About 1,tiOO
f e e t a f t e r you passed t h e last monzonite outcrop, you
have low ledges on the south side of the trail.
So take off
a.t examining rocks.
characteristicblocksthrough,
whatever you observe.
By
now
you are an old hand
your pack, get out the
hammer, break a few
and examine them.
Then, as nsual,write
down
Now you should be so experienced that youdo not need
any further explanation.
The minerals i n t h i s rock you have seen before.
Perhaps the grains are of different size or color from those in another rock;
but that i s common.
Next t r y t o aecide khether this rock
the Pierre shale,
or structureless, like the
i s composed of layers, l i k e
porphyry.
It doesnot make very
much difference what you may decide i n t h i s p a r t i c u l a r outcrop.
t h e main thing i s t h a t you t r y t o observe the rock
As always,
as carefully as you can,
and record w h a t you see.
About 60 feet farther up the trail, you pass more ledges.Repeat
your observations,
and write down what you fina.
Climb up on the lar&
ledge
-9d i r e c t l y n o r t h of the creek, and examine it. Don’t hurry.
e
of time on the rocks.
When you comedown
s e t t l e d t h e matter of layered
should have seen the coarse,
VS.
Spend plenty
from t h a t ledge, you should have
structureless,unlayered,rock.
and fine-grained beds,
You
and you should have a
If
p r e t t y good idea of w h a t kind of rocks make up most of that c l i f f .
.
.
i n doubt, consult the chart
on page 32 of your Merit Badge Booklet.
Did you also observe and record i n your book whether the layers
l i e horizontal or, i f Fihey are t i l t e d , i n which general geographic direction
they are dipping,
and at about what degree of inclination? Be sure you
write down a few words.
Later, you w i l l need t h a t information.
West of t h i s ledge, the North Fork
MiddleFork,
of Cimarroncito Creek joins our
and a trail follows the North Fork to an
abandoned mine.
We
stay on the main trail, because from now on we shall have much t o observe
and record. Directly
on thenorth
west of the mouth of NorthFork starts a h i l l s i d e
bank of MiddieFork.
and record the usual things, colors
o f
Examine t h e many outcrops of rock on it,.
of the rocks, types of layers, attitude
the layers, composition as 8itLa as you canobserve
If time permits, climb
around.
Bynow,
it.
up a short distahce on this slope, and look
you have seen a s t r i p of country, nearly
westerly direction1
6 miles i n an east-
You are already among f a i r l y h i g h mountains,and
you
have been patient enough t o make careful observations from one outcrop t o
another.Gradually,
some rewards f o r that patience w i l l come in.
You want
t o know, as every geologist does, why t h e mountains are there; why they are
so high; and by w h a t kind of a mechanism such hage masses of rock are b u i l t
up i n t o a chain of mountains.
Take out a clean sheet of paper, or a page
i n yournotebook.
Draw a thin pencil line sloping gently
down t o the right,
and write a W j u s t above the l e f t end, and an E at
the
right
one.
from t h e l e f t
-10-
Thus:
w
T h i s l i n e may represent roughly the earth's surface,
a.s it. slopes from
where you stand eastward t o t h e h i l l s i d e with the minette and Pierre
shales.
Look up i n your n o t e s i n which direction the shales d i p at the
minette hill,
the "skyline",
and at about howmany
degrees.
Now draw a.few lines below
on the eastern portion of your diagram, t o r e p r e s e n t t h e
dipping Pierre shales, thus:
d
They dip northeast,
at about 5-8",
t h e r i g h t i n your diagram.
so t h e l i n e s
should be i n c l i n e d t o
The exact angle of the dip i s not important at
this moment, but keep it gentle. In the
middle of t h e diagram, you can not
draw apything because t h a t is t h e 5-mile s t r e t c h whereyou drove through,
l
you remember that from t h e
and d i d n o t s t o p t o examine any outcrops. But
and, as yau started out on t h i s
distance you saw P i e r r e shale ledges there,
trail, you passed that outcrop of Pierre shale,
Base Camp.Look
100 f e e t west of Cimwroncito
up i n your notes at about howmany
that outcrop dip, and i n w h a t general direction.
t o observe and recordthat!
degrees the shaLe beds i n
Don't t e l l me you forgot
For that serious omission, you should be
required t o walk r i g h t back t o t h a t ledge, and complete your notes.
But fortunately, you axe as y e t a beginner, and it takes time before
you remember everythingin a new occupation.
missing f a c t s and figures w i l l be supplied:
100 f e e t west from t h e Camp, dips at about
So, j u s t this one time, t h e
The dark brwish-gray shale,
36 degrees downward t o the
-11-
northeast. Better stop there
a
when you return from t h i s t r i p , and make
s u r e t h a t this i s correct.
About 113 inch from the l e f t i n om diagram, we draw l i n e s
For thetimeib&ing, l e t
sloping down t o t h e r i g h t at about 35 degrees.
us omit the porphyzy i n o w traverse, and now, at t h e l e f t (western) end
.of our
diagram, we draw the variegated shales and sandstones that are
before us, also with t h e i r average dip angles, thus:
w
Now you can see something very interesting:
The layers of
P i e r r e shale and sandsbone d i p s t e e p e r t o the northeast as you follow them
from e a s t t o west.
I n your Merit Badgebook,
you have read that nearly
a l l layered rocks:.are depositedoriginallyinhorizontal
zontalbeds.
Our strata areinclined.That
or nearlyhori-
means, they must have been
tipped up i n such a way that the western ends of t h e beds were raised,
or the eastern oneslowered.
i n f r o n t ofyou
It shouldbe
clear, also, that the
underlie the ones fa&ther east.
a specimen of t h e yellow, green,
So, i f youwant
or gray sandstone beds before
strata
to obtain
you(shown
w i t h d o t s i n diagram) at the minette h i l l , 6 miles e a s t , you'd have t o
d r i l l , and some hundreds or thousands of feet below the surface you are
l i k e l y t o run i n t o them, thus:
you s t r e t c h o u t your r i g h t hand,palm
left.
flat, f i n g e r t i p s p o i n t i n g t o t h e
Now raise your l e f t f i s t slowly yrom underneath your r i g h t f i n g e r s .
-12-
The fingers are forced to
e
and steeper the farther
bend, and your palm will be tipped up steeper
resembles w h a t has happened t o t h e rocks here,
A s you continue west,
wouldyou
If that picture
you raise your l e f t f i s t .
you can make a few guesses:
i n w h a t general directions
and pass more layered rocks,
do you expect the
expect the layers to dip? Generally speaking,
layers farther west t o dip more gently, or steeper?
O u r guesses and experiment are,
of course, not quite adequate.
For one thing, we have l e f t out the porpwry
. But at the moment, it looks
as if the high mountains west of you have been pushed up from underneath, somewhat l i k e your f i s t underyour
flat palm.
Now l e t ' s continue
on our trail.
Nearly continous,
trail for the next
low outcrops along the
300 geet display a variety of purplish sandstone, shale,
e
a.nd s i l t s t o n e
beds, with a few very fine-grained calcareous lenses.
where t h e trail crosses over t o the south side
at the ledge just
creek.
Be sure you stop
of t h e
What you see here i s most interesting and important f o r t h i s
entire t r i p .
You see layer upon layer dipping
easterly direction.
rock appears;
in the familiar north-
But at the last 7 f e e t or so, an entirely different
however, as you break fresh surfaces from t h i s ledge, you will
recognize it at once as the rock you saw
porphyry".There
is no doubtabout
g mile
ba'c-k: "quartz-monzonite
it. Thesame
b i o t i t e , and hornblendeneedles,again
someof
whitish feldspar crystals,
the peculiar pebblelike
quartzes, and a dark gray groundmass.
Now be sure you examine the surface there the
rocks meet.
It i s spoken of as thecontact.
tions with caie,
e
as you should, you'll notice
two different
If you make your observathat both the porphyry
and t h e shaly layers change as theyapproacheachother.
in the shale
note there?
The changes
should at once r e c a l l which other outcrop?
Did you find aboutthe
sme thing here?
What d i d you
If you do, how
-13wouldyou
0
i n t e r p r e t t h e change i n the shaly rocks?
If you look up
your notes from that o t h e r t r i p , all the details w i l l come back,and
you have t h e s a t i s f a c t i o n t h a t at two entirely separate places you can
check the same important change i n a rock.
Very probably,then,
the cause
So far, you had t o talre my word f o r
was a l s o the same i n b o t h pla.ces.
it that the monzonite porphyry was an igneous rock that was once very hot.
Now you have before you confirming evidence.
nearly a thousand degrees Before
The shale had t o be heated
it turned into the gray, dense hornfels.
So t h i s does make some sense, eventhough a l l the rocks are now cold.
If you continue geological studies,
your job i s to reconstruct processes,
sequences of events.
you will find, over and over, h
ta
A
movements, causes and effects, and
It is this reconstruction that permits you t o b r i n g
the earth's crust truly to life,
andyou
can depict stage after stags
in the evolution of a mountain range, a former volcano,
A s you examine the contact surface
or even a continent.
between the quartz-monzon-
i t e porphyry and the baked shale, you notice two things: the surface runs
p a r a l l e l t o the beds of
the feldspar phenocrysts
shale, and within some 5 inches from the contact,'
become smaller and smaller, and the dark gray
goundmass increases in volume correspondingly.This
mon behaviorofigneousrocks.
i s a f a i r l y com-
It i s explained by saying that the
molten lava that came f i r s t in contact with the cold rock, lacked the
large feldspar crystals,
or that only small onescould
be squeezed i n t o
an o r i g i n a l l y t h i n c r a c k i n the shale, and froze onto i t s wall.
After crossing the creek,
across monzonite.
Then,on
you can walk f o r about, 250 f e e t
the south side of t h e trail, comes another
important outcrop which you should examine j u s t as carefully as the
0
last one.
ledge.Inthe
You w i l l see that it i s about the "mirror
first, theshalelay
monzonite l i e s on top of the shale.
image" of the last
on top o f ' t h e monzonite, now the
The shale i s againcontact-meta-
morphosed (or "hornfelsed") at the contact,
a.nd if you will examine,
-14as you were asked, the entire ledge,
you will find, as a special, local
i s quartz,stainedred
contactmineral,scarlet-redjasper.This
Don't demolish t h e e n t i r e c l i f f
ironoxides.
year, too,
on i t s account.
Next
some Scouts w i l l w a n t t o collect a l i t t l e b i t of it.
Before you leave the ledge, take out
and t r y t o extend your cross-section diagram
it shows the Cretaceous Pierre
your paper and pencil,
t o t h e westward.
sandstone ledges are, near the mouthof
d i p s where the
North Fork Cimarroncito
at the minette hill.
and t h e imaginary d r i l l hole
Creek;
Now draw t h e sky-
If you have no room, start a new diagram
line farther to the west.
which the right (eastern)
p a r t of your f i r s t diagram.
p a r t coincideswiththe
l e f t (western)
Draw a l l the purplish, gray,
and yellowsands-
tones and shales that d i p northeastwmd between the mouthof
and the ledge
So far,
shales at the minette hill dipping gently
eastward; t h e 5-mile gap i n observations; the steeper
o f
by
where the shale r e s t s on the monzonite.
estimate dip angles fairly well,
North Fork
Now, i f you can
you will find that in both outcrops the
contact between the shale and t h e monzonite has almost exactly the same
dip angle, to
w i t , 37-40',
down to the northeast.
As you see it at the
is p a r a l l e l t o the shale or hornfels beds.
jasper ledge, the contact
I n your section, therefme,
you can draw two l i n e s having the same d i p
as that of the shales, and the rock between them w i l l be monzonite
porphyry, not shale.
shapeof
It should be c l e a r t o you t h a t t h e porphyry has the
at the same angle and i n t h e same
a layer, or plate, dipping
direction, as thesurroundingshales
and sandstones.There
is a name f o r
an igneous mass that has the shapeof
a p l a t e p a r a l l e l t o t h e bedding
planes of layered rocks. You'll find
it i n yourMerit Badge book.
Estimate the thickness
add that figure
of t h i s p l a t e of quartz-monzonite porphyry,
on yourdiagram.
and
Be sure not to confuse the distance
between the two contacts, as you walk it on l e v e l ground, with the distance
of an imaginary l i n e at right angles to the
upper and lower contact planes.
-15Bynow,
a
you should r e a l i z e that i n your section a great many
masses of quartz-monzoniteporphyry a r e involved.
large cliff north
of the reservoir,
just east of t h e base camp.
c l i f f , you may as well know, was porphyry.
were concealed.
mass, that dips northeast,
Bynow,
as i f it were a layer of a sedimentary rock.
many tall, gray c l i f f s that
on the north and south sides, are apparently a l l
If we could remove a l l t h e porphyry, leaving only
composed of porphyry.
around us would i n a l l probability
the soft shales, the entire scenery
be muchmore
But the contacts with the
Now you have passed a large sheet-like
also, you will r e a l i z e t h a t t h e
surround the creek
This
Then you passed that mass,
about 100 f e e t a f t e r s t a r t i n g on the trail.
layered shales
F i r s t , you saw t h e
subdued, resembling the rolling foothills farther east.
You can see now that i f one of two adjoining regions is composed of a
e
r e s i s t a n t rock, the other of a less r e s i s t a n t rock, it stands t o reason
that the first region will have a highersurface,
other.This
i n geolom.
i s animportantprinciple
discussed i n yourMerit
i n general,thanthe
You w i l l find it
As a l l principles, this
Badgebook.
Perhaps t h i s paragraphcauses
has exceptions.
you some confusion2 A while
back, you drew a cross-section, showing the Cretaceous shales dipping
steeper on the west; and with your hands you made a simple experiment
showing that it looked as though the high mountains t o t h e west of you
had been pushed up.
mountains were made.
T h a t seemed perhaps a plausible explanation ofhow
Now comes quite another principle into
the resistance of different rocks.
this story,
If you have resistant rocks
west, and soft rocks on the east, then
too, you might expect hi&
on the
mow-
t a i n s on the west side.
0
A l l t h i s need notconfuse
you.
Rather, it should make you
aware that Geology i s a complicatedscience.Like
a machine t h a t con-
sists of many p a r t s , each of which has a c,ertain effect on the workings
of t h e whole mechanism.
You must study a l l parts before you can
sm
-16-
*
We know that all kinds of
t h a t you understand t h e e n t i r e machine.
factors have eniered i n t o the formation of t h e Rocky Mountains.
meet manymore
as we go along.
The creek and trail make a curve,west
The shale i s again interrupted by monzonite por-
of the Jasper ledge.
phyry of which you pass some tattered ledges
more quartz than the
monzonite outcrops east.
northwest,gray,sandstonecropsout.
on your right.
It d i p s againnortheast,hut
i s concealed.
or it mighthaveany
rockcould
be anothersheet,
not t e l l .
The sandstone i s againinterrupted
again tan,
other shape.
The igneous
You can
by porphyry, some 100
It i s apparently a small mass only,because
soon you see
or p a l e brown shale, and then come several.ledges of a purple
sandy Shale, dipping at about 35” northeast.
you can see l i t t l e sparkling blebs.
@
They have
About 150 f e e t f a r t h e r
the contact with thequartz-monzoniteporphyry
e e e t west.
You will
On some beddingplanes,
They are white mica, or muscovite.
It d i f f e r s from t h e brown o r green b i o t i t e i n t h a t it lackstheiron
oxide, and therefore has
no color.
you w i l l note in these outcrops that not a l l the layers are
p a r a l l e l t o eachother.
Some groups of beds are beveled by others, thus:
This i s called“cross-bedding”.
You can find it where sand has been
blown about by the wind, and heaped up i n dunes.
You also find it where
swiftly flowing water c a r r i e s much sand, silt, or gravel, and has t o
force i t s way around obstacles.
e
It will then push the sediment i n many
small channels which may cross each other
as time goes on, and the sand
degpsrGted yesterday i n one channel, may today be wornawayby
channel.Nearly
a l l cross-beddedsediment
another
was depesitedinshallow
fiadd plains by river water, or blown together by wind.
SO
we learn here
-17something about the mode of origin of t h i s rock.
A t the base of these cross-bedded layers, you find others
t h a t a r e composedof
across.
rocks.
f a i r l y well-roundedpebbles,
I n your Merit Badgebook,
you will find a r e f e r e n c e t o such
If the cross-beddedsandstone
or through accumulation of
some nearlyinch
was formed i n e i t h e r f l o o d p l a i n s
sand inddunes,
you can reach a conclusion
a s t o which of these alternatives i s the more probable one f o r t h i s
particular group of beds.
For some 150 f e e t t h e t r a i l passes purple shale in
outcrops on t h e r i g h t side.
small
J u s t a f t e r you pass a curve i n t h e t r a i l , '
the shale is suddenly interrupted f o r some 12 f e e t by a different rock.
You a r e now s o experienced i n recognizing the Philmont rocks t h a t it takes
you j u s t one minute, a f t e r breaking a fresh block of t h i s rock, t o recognize
e
it as another mass of quartz monzoniteporphyry.
And you need no reminder
not walk on before you have t r i e d t o determine the shapeof
t h a t youmust
t h i s r e l a t i v e l y small mass ofporphyry.
This i s madesomewhat
easybecause
fromthe t r a i l you can see the porphyry extending upward along the hillside.
If youhave
a. compass, you can determine t h e d i r e c t i o n i n which it runs.
If not, use the position
.
of the sun t o estimate the general geographic
direction1 Would you saytherock
it horizontal,vertical,
must determine i n whichof
do that, youmust
has the shape of a p l a t e ? If so, is
or inclined? If it i s inclined,ageologist
the two possible directions the plate
ofcourselook
for the contact plane. Put
and mind t o it, and you will find the answer.
By
now
dips.
To
your eyes
you w i l l a l s o know
whether t h i s mass should be called a dike, or a. s i l l .
You are now faniliar with mostof
on t h i s t r a . i l .
As you continue, you pass several more masses of quartz-
monzoniteporphyry,
probable shapeof
the rocks you w i l l encounter
and should make a ne f f o r tt o
each mass.
determine the most
If you were ppfd t o map the geology of
this ravine, you would have t o climb up the walls every time you pass a
-18porphyry mass, t o determine and measure i t s exact orienta.tion.
Not a l l the
contacts are exposed, and i t ' s quite a. job t o determine the shape of the
concealed contacts.
But for the sake of accurate and reliable mapping
t h i s must be done.
Between the monzonite porphyries, you pass again many outcrops of reddish, purple, or buffsandstone.Associated
with them
A good one is on the northwest side of the
ase layers ofconglomerate.
trail, about 100 f e e t above the "Stone Fa.ce" masker.
the diameters of the largest pebbles i n t h i s rock.
8he rocks.of these pebbles.
Measure, or estimate,
Take a good look at
Do theylookfamiliarto
you? Whether they
do or not, a conglomera.te w i l l always i n t e r e s t you i f you study Geology.
We go into picture galleries
and museums, or may openbooks with pictures
showing w h a t clothes people wore, hundreds or even thousands of years ago.
On the Greek temple f r i e z e s , we can see scenes showing people talking B r
arguing; we can see what gadgets they used f o r weighingmerchandise,
pencils f o r writing on papyri, what buckles they woreon
Now a conglomerate i s something j u s t 8,s precious.
what
their sandals.
It i s something l i k e
a photogcaph of a busy railroad station, many millions of years ago.
O u r tna.ins are, of course, the streaming wa.ter p a r t i c l e s i n a. former creek,
pebbles t h a t have a l l been
and the passengers are the thousands of rock
urged on, pushed about, and f i n a l l y dropped by the water t r a i n .
they come from, how far d i d they travel before they
Where d i d
were deposit&?
If you
are waiting for a friend a.t a r a i l road station, you can give an exact
anmer only for your friend, because you know where hecomes
and how far he traveled.
For the other passengers, unless they
turban or a k i l t , youwould
a
not know tha.t.
from,
wear a
It i s very much the same when
you study the pebbles i n a. con.@lomerate. If youknow
that there i s a, ledge
at such-and-such a place of t h i s or that rock which l i e s before you as a
pebble or boulder, then
you can assume that some time ago the stream that
collected a l l these pebbles, picked
up someof
them at the v i c i n i t y '
-19of the place you know.
But if youhave
neverseen
a fock, you can not t e l l
where that ancient stream acquired this material.
Right now, you are not yet familiar with a l l the rock formations
of the Philmont Ranch.
But i n another week or so, you w i l l be.
if you are energetic, examine some of these pebbles carefully,
down at l e a s t a few Brief notes on the color, grain size,
Just now,
and write
and other striking
c h a r a c t e r i s t i c s of some of the pebbles. SEiould you later find outcrops
of rocks tha,t resemble the ones
you see before you i n pebbles, you can
s t i l l get an answer t o your question.
This l i t t l e search among the pebbles will make you r e a l i z e
that much of a g e o l o g i s t ' s a c t i v i t y i s similar t o t h a t of a detective
who constantly is on the lookout for clues
apprehensionofthefelon.
0
and h i n t s that may lead t o t h e
O u r geologicalfelonsare
we want t o know where that formerstreamgot
tofindout
many:
Right now,
i t s pebbles.Before,
we wanted
where tat. molten lava was going t h a t made the many porphyry
dikes, or that minette lava that passed through the
headquarters.
Is it hiding
8
volcano from us? If there was one, d i d it
have a grand plan up i t s sleeve, perhaps,
up into the cold
h i l l l m i l e west of
t o push the Cimarron Range
of thehigheratmosphere?Like
a good detective, you
don't jump a t conclusions, but wait till a l l the clues converge toward a
story that canbechecked.
I n any case, you already have quite a few
. .
less than 2 days i n t h e f i e l d . T h i s
r e l i a b l e and interesting clues, after
i s rapid progress. There are regions
where a geologist may qpend days, weeks,
o r even months without getting anywhere.
h i l l s and valleys may becovered
neversee
a
outcrop during an entire field
example,
by deep s o i l , so continuous t h a t you can
a fresh outcrop ofrock.
working along the coastal plain
In the hGid tropics, for
A few years ago, a geological party,
of northern Alaska, paw exa.ctly one rock
season!
If you continue on t h i s trail, you pass another massof
porphyry some 300 feet west. Notice the larger
amountof.
gray fine-grained
-20-
groundmass i n it, and the small amountof
quartz.
several specimens i n which the darkhornblende
green.
You w i l l probably find
c r y s t a l s are a bright
The green minera.1 i s calledepidote.(Transla.ted
wordmeans,
"given in addition to",
from Greek, the
and goesback t o an incident, about
150 years ago, when the famous French mineralogist and prelate, Hauy,
experienced great difficulty in determining the particular crystal
All specimens hadone
of t h i s minera.1.
mineral'ssuspected
symmetry.The
system
crystal surface tha.t destroyed
problem was f i n a l l y solved,but
ammoying plane was remembered when the mineral was named.The
the
the
c r y s t a l s you
see, are so small, however, t h a t you are not likely to recognize crystal
surfaces.)Epidotehasaboutthe
sme chemicalcompositionofhorn-
blende, and under certain physical conditions, the
molecules of hornblende
will change over into those of epidote.
0
Fromnow
on, muchmore monzonite porphyry i s i n evidence.
Soon, a l a r g e c l i f f of t h i s rock forms thenorth w a l l of the canyon,and
the coarse debris sandfrom i t s ledges strews the slope t o such an extent
that you can not see any other rocks that may be buried undernea.th.
Never-
theless, if a l l the debris (Also c a l l e d t a l u s @ geology)could be removed,
you would probably f i n d the same reddish and purple sandstones andconglom-
erates that you saw farther east.
I n your diagram, you maynow
f a s west a s youwent;
as
add another section, extending
i f your observations on the contacts of the various
porphyry masses are correct, you can add these as l i n e s having the appropriate
directions of dip.
Some, as you recal1,dip t o the northeast, like
sedimentaryrocks.Othersdipacross
~
~
the porphyry has broken across
these
beds
in
between the layers in other places.
I
the layers.
world do that.
the
So it looks as though
some places, and squeezed i n
Volcanicrocks
i n many parts of the
If you continue t o the Lambert or Cypher's Mine,
you
see
practically nothing but porphyry varieties, some of which have muchmore
quartz, and the feldspar crystals do not show the cleavage well, but look
I
chalky.
We will discuss the rocks at the mines on another page.
TRAIL FROM ABREU BASE CAMP WEST ALONG RAYADO CREEK
e
-1-
*
To reach Abreu Camp, you drive west from Carson Maxwell Ranch.
Again, you start i n t h e e a s t e r n f o o t h i l l b e l t ,
whereyou reach Abreu Camp.
and a r e deep i n the mountains,
As you drive west,
on the north and south,thoughnot
you find the skyline
everywhere horizontal.
flat
From a n e a r l i e r
t r i p , you know what these flat-topped mountains a r e c a l l e d i n t h i s p a r t
the United States.
top.
But you don't know w h a t kind of rock crops out
Whatever it is, it must be veryextensive.
ward to the left (southwest).
There, individual mountains p r a c t i c a l l y
large plateau coincides with the southern
edge of t h i s
boundary of Philmont
Below the plateau cap rock, north and south of lower
you have smooth, relatively featureless slopes.
e
at the
Keep your eyes a l s o for-
disappear in one large plateau. Incidentally, the northern
Just rock:
of
Ranch.
Rayado Creek va.lley,
You can suspectthe familiar
space. thef i l l out
Before you leave, look around
Abreu BBseeC@@y On the north,
across the gorge of Rayado Creek, i s a magnificent cross-section of a
p a r t of the same formation that accompanied you since you drove over from
Ranch:
Carson Maxwell
south
but you can pick up large boulders
of the Camp, t h e p i n e s a r e f a i r l y t h i c k ,
Take a good look at them.
on the slope.
Directly
Break off, as asual, a f r e s h
surface, and examine it. To make sure you examine the right rock, look f o r
those that have many vesicles and cavities, are of rather dark gray,
times purplish color,
and are p r e t t y hard at t h e blow of t h e hammer.
someFresh
surfaces show, a p a r t from the many l i t t l e holes, a uniformly fine-grained
rock that does not t e l l you very much of i t s composition and texture, except
t h a t it i s not layered.
Every now and then, however, a surface in sunlight
w i l l show a few small, weakly reflecting: grains.
A s you can not determine
the rock on the basis of so few c r i t e r i a , you may be t o l d that t h i s r o c k
i s basalt.
Next to branite, limestone
abundantrock
and sandstone, it i s about the most
i n t h e earth's crust. This
pa.rticug& basalt i s fine-grained,
-2and you need a,microscope t o identify the individual minerals.
one, you couldrecognizethemineralsfeldspar
Greek, pyroxene means "friend of Fire",
molten1a.m.).Rarely
If youhad
and pyroxene (translated from
i n r e f e r e n c e t o i t s growthfrom
do they form phenocrysts,about
1/8 inch long.
mesa, southwest of you, and
Keep i n mind, then, that the large
always on the south bank of Rayado Creek, i s a. large f l a t p l a t e of Bksalt,
a t r u e lava. flow, i n every respect similar to
i n t h e Hawaiian Islands, Iceland,
or other basaLtic regions
Once you recognize the typical appearance
that the north slope
the ones we can see erupt
of RayadoCanyon,
of the earth.
too, is in places crownedby ba.salt
and, as you can
cliffs, but they are less continuous than the southern ones
see from several points of vantage,
will see
of t h i s basalt mesa,you
the basalt on the north side
of the
canyon overlies the gray Pierre shale.
a mile, the trail leads through slope debris,
For over
allow you t o g e t a clear picture of the geologyof
p i n e f o r e s t doesnot
underlyingrocks.
and t h e
the
However, reconnaissance work has shown t h a t t h e P i e r r e
s h a l e i n a l l probability underlies the canyon.
c l i f f of a hard rock.
Finally, you pass a l a r g e
With l i t t l e e f f o r t , you can ma,ke out the layers in
t h i s rock, and examination of fresh surfaces will convice you that t h i s is
not the Pierre shale
any m0re.k
.If you r e c a l l your observations along the
t r a i l leading westward
from Cimarroncito Base Camp, you w i l l see that you encounter the same
sequenceofrocks
dipping northeast,
*
as you go from e a s t t o west:
f i r s t a large mass of shale,
away from t h e mountains (on t h i s trai$,
YOU
have been
to
unable t o study the a,ttitu.de of the shale layers, but here, too, they dip
t h e e a s t and northeast); then, layers
grained homogeneous rock,dipping
of a. hard, gray or yellowish, fine-
more steeply eastward.
If youhad
time,
you could climb up on this steep ledge on the north bank, &d if you follow
it across several other
canyons, youwould
come out a.t the ledge by the
Cimarroncito trail, about 1,100 f e e t west of the Base Camp.
The outline of
-3that trail d i d not t e l l you very much about t h a t rock. But
Shall
at theCimarroncito
assume that you have examined therockcarefully,both
t r a i l and t h i s one, and you maynow
I
be t o l d t h a t th$S i s a very famous
and important formahion:.of t h e e n t i r e Rocky Mountain region, the Dakota
sandstone.
Through the Dakotas, Montana.,Wyoming,
Mexico,and
Arizona, the Creta.ceous shales
sandstoneformation.
Colorado, Utah, New
r e s t n e a r l y everywhere on t h i s
As you can s e e i n t h e c l i f f b e f o r e
e a s t a t about 30-40 degrees.
You can see exa.ctly the
you, the beds dip
same on t h e e a s t
slope of the Laramie Range i n Wyohing, along the entire Front
Range of
Colorado, and i n t h e f o o t h i l l s of the Black Hills i n South Dalrota.
In most sections, the Dakota sandstone i s a porous rock.
Therefore, it acts like a,wonderful receptacle for rain water that flows
off the east slopes of the Rocky Mounta.ins. The rainwater flows into the
which conducts it along i t s bedding planes
pore spaces of the sandstone,
deeper and deeper i n t ot h ee a r t h ' sc r u s t .
If you stand i n western
Eebraska, where water i s scarce, and d r i l l through the Cretaceous rocks,
you h i t t h e Da.kota sandstone, and since the surface of the Great Plains
i s much lower than the surface at t h e f o o t h i l l s o f t h e
the water in the
Rocky Mountains,
Dakota sandstone will rush to the surface, cold
and
f i l t e r e d by nature, and provides w h a t i s known as flowing wells:
*
You will understand now t h a t t h e sequence of layered rocks,
a.nd t h e i r
structure, as you observe and record it in the various canyons on Philmont Ranch, a r e p a r t s of
8,
large and persistent geological plan that
-4-
dominates the entire eastern slopes
@
product of it, theGreatPlains,
of the Rocky Mountains; and as a by-
floom North Dakota t o western Texas, a r e
providedwith f a i r l y adequate amounts of excellent ground water.
Theamount
would be even l a r g e r had t h e e a r l y s e t t l e r s and communities shut the valves
of t h e i r Elowing wells when they did not
them were permitted, year
after year, t o flow t h e i r f u l l amount of wa.ter,
the early settlers assming there
Since the f i r s t decadeof
pumps were installed.
hundreds of
need water. Instead,
was an inexhaustible supply
this century, the
amountof
of it.
water decreased, and
When even pumps d i d not supply enough water, it
became clear that a,watershortage was imminent.
Since that time, con-
servation measures have been applied, and now the amount of groundwater
i n t h e Great Plains i s generally adequate, but
s t r i c t r e g u l a t i o n s of
m a x i m u m discharge per well and county are i n e f f e c t .
Whereas the eastward-dipping Cretaceous
geologicfeature
of theeasternslopes
strata are a. c h a r a c t e r i s t i c
of the Rocky Mountains, the many
not.
monzoniteporphyry dikes and s i l l s which you s e e i n t h i s a r e a , a r e
Clusters of volcanic rocks, east of t h e c r e s t of the Front Range, are
found i n t h i s northernmost part of New Mexico and the adjoining portion
ofColorado,
see, about
a.s well as i n Montana.The
Spanish Pea.ks, which you aan
70 miles north of the Philmontmountains,
of these igneous rocks.
a r e two great eenters
But in most ofColorado and Wyoming, you can
drive o r walk a l l the way up t o t h e c r e s t of the Front Range without
seeing volcanic rocks.
For some 2,000 f e e t west of t h e c l i f f ofDakotasa.ndstone,
there ase no outcrops by the trail.
sandstone.Notice
0
Then you pass another ledge of
that it too is composed of l a y e r s t h a t d i p ea.stward
a t about the same angles as the Dakota sandstone.
It shouldbe
clear to
you t h a t t h e 2,000 or so f e e t between these two prominent c l i f f s are
underlain by other rocks which here happen t o be covered by t a l u s and
vegetation.
If you were t o map the canyon, you would have t o leave the
for possible outcrops of these rocks.
t r a i l , and search both slopes
0
Perhaps t h e r e are scatteredexposures,perhapsnot.
It mightbe
ne-
cessary to spend several days i n such a search, yet you might find
nothing.
If you a,re i n danger of getting discouraged by suchanexperience,
you had b e t t e r r e c a l l a n i n c i d e n t i n t h e
l i f e of Thomas A. Edison.
the morning t r a i n from Menlo Park t o New York,he
with other passengers
him:
whom he knew.One
On
used t o s i t together
morning, one of them said t o
"Mr. Edison, I have noticed you look a l i t t l e unhappynowadays."
Mr. Edison,
"Well", said
"For the past 5 weeks I have t r i e d 325 d i f f e r e n t
metal filaments hoping t o f i n d one t h a t would be incandescent i n an
e l e c t r i c bulb.
Notone
of them is."
with Edison, and the colossal wasteof
of time?"shotbackEdison,
these 325 alloys
0
His friendexpressed h i s sympathy
time.
"What doyou mean, waste
"It was no wastea.t
all.
Now I know t h a t
won't work."
If you are wondering w h a t the concealed area may contain,
it may pay you t o look up your notes from the Cimarroncito trail.
below the Dakota sandstone, i. e., west of
of gray,greenish,
see nowwhy
trip.
it, you passed quite a s e r i e s
and purplish shale and sandstonebeds.
You can
it pay t o have complete notes on rock outcrops from every
As a matter of f a c t , t h e s e r o c k s a r e p r e s e n t i n t h e
too, but here
happen t o becovered
up by t h e t a l u s debris.
RayadoCanyon,
The c l i f f of sand-
stone at which you now a r e is, of course, an older rock than the
sandstone.
There
If you don't believe this,
Dakota
draw again a cross-section, as you
did at the Cimarroncito trail, draw your skyline, mark W and E i n t h e
usual way, and draw t h e Dakota sandstone, dipping east
Then leave a space of about
stone,dipping
at about 30 degrees.
2,000 f e e t f r e e , and draw the secondsand-
at about 45 degreeseast.This
bed, obviously,underlies
the Dakota, and it i s thereforeolder.
As you continue west,
be few, but after aboutmile,
upRay&do Creek, outcrops continue t o
you w i l l notice small chips and boulders
-5of a reddish and purplish rock.
outcrop of t h i sr o c k on thesouth
Keep an eye onthem.Soonyou
t o make out i t s composition.
record whether the rock i s layered, about
and i n which direction.
hand.
If you have a hand lens,observe
Note and
how steeply the layers d i p
Prominent i n t h i s rock are pink grains
2-5 millimeters across.
cleavage,about
It i s somewhat
bank of thecreek.
disintegrated but s t i l l goodenough
pass an
with
Take a few of them i n t o your
them.
Does the mineral have
one cleavage system, or more? Right you are, two cleavagesystems,
intersecting a t about right angles.
Other tests you can not well make,
I n addition, you
so you may as well know that the mineral i s feldspar.
will probably guess correctly w h a t the many glass-like colorless grains
~
are.
I
I n short, you have a layered rock composed f o r t h e most p a r t of
quartz and feldspar grains.
Such a rock i s called arkose,
or feldspathic
sandstone.
0
It should be c l e a r t o you t h at ht ri so c k
must have been
derived from some other rock that was p a r t i c u l a r l y r i c h i n t h e s e two
I
minerals.
addition,
In
it has many l a r g e r pebbles.
They, too, are
~
reddish, seem t o be aomposed of quartz and feldspar.Others
and themselves layered.
If you kept youreyes
a r e dark,
open t o a l l the various
rocks at and near the trail, you w i l l now recall, that yrru have passed
,
~
many boulders in the stream bed that f i t this description.
therefore, as if the source rocks for the arkose crop out
of you.Watch
from now on the boulders in the creek,
It seems,
somewhere west
ana
you can not f a i l
t o spot the pink or red ones, as well as the dark greenish-gray Layered
ones,
They are altogether different from rocks you have so f a r seen i n
any outcrops.
If you keptaccuratenotes
on bouldersseenabout
mile,
west of Cimarroncito Base Camp, you w i l l f i n d descriptions that f i t your
bouldershereclosely.Apparently,then,
somewhere i n t h e more westerly terrain, but
crops
Of
a whole formation of rocks i6:
you have not yet seen out-
it. In geological work, it i s important t o notice a l l kinds of
-6loose blocks and rock specimens.
With experience, you learn
much time through such incidental observations.
t o save
No geologist has
so
much time that he could hope t o v i s i t every ledge of rock i n each region.
He saves time by visiting
the l a r g e s t and most rewarding outcrops, and
by arranging his f i e l d t r i p s so that he passes the maximum number of
rockformations
in the least
time.
To become acquaintedwith a l l the
formations on the Ranch, you know now you must extend your t r i p s f a r t h e r
west.
A t the moment, then, you axewalking across a formation of
arkoses,purplesandstones,
and shales.
Had you more time t o go off the
trail youwould find numerous outcrops of these rocks,
It i s t h i s s e r i e s of rocks, older-than the Cretaceous
a l l dipping east.
system, that you
studied on your t r i p west from gsmarroncito Base Camp.
A short distance west, you pass on the north side of t h e
creek a l m g et a l u s
+ope of purplish basalt boulders.
The rock'cropsout
at the rim of the canyon, and remains i n evidence f o r several miles.
About at the west end of t h i s t a l u s mass, you can see forward t o the right (north canyon wall), several large conical red pro-
montories.
A s you approach them, between the pines, you see crags
grayish color.
of
If they are not too f a r above the trail it may pay you
t o climb up t o one of them.
It i s a fair guess that i f you had never i n your l i f e seen
an automobile, and t h e first one were shown you a f t e r every single b i t of
its s t e e l , btass, upholstery, rubber,
and glass had been smashed t o bits,
and the whole shapeless i m p cemented with Duco, you are n o t l i k e l y t o
*
recognize it as an automobile, t o saynothing of the brand!
you now approach, are exactly this, except
used.
The ledges
that ordinary rocks have been
For nearly two miles,everysingleledge,despite
i t s r e s i s t a n c et o
weathering, t u r n s o u t t o be an extraordinarily crush$& and recemented rock,
SO
u t t e r l y d i s t o r t e d and fractured that you can not t e l l much about it.
-7Every block or specimen you touch with the
hammer, crumbles i n t o t i n y bits
and slivers, and you quickly realize that t h i s rock has been as completely
smashed as a b o t t l e you hurled against a wall.
If you have never seen such
a rock, it i s worth while t o
examine it carefully, and ponder t h e s i t u a t i o n for a few minutes.
To crush
with a sledge hammer a boulder, about 1 cubic foot in volume, takes a strong
man about 10 minutes.
A toughrock
would take much longer.
Here, you can
walk along completely crushed,rocks for nearly 10,000 feet, and if you have the
time you can climb up about 400 feet, and the crushing
If a tunnel were driven into the northern
the samemashed
would not diminish.
canyon w a l l , it would encounter
rock f o r probably more than a mile.
And my guess i s t h a t t h e
same contition continued downward for well over 10 miles.
has 5,280 x 5,280 x 5,280 cubic f e e t of rock.
One cubic mile
O u r strong man would r e a l l y
wear himself out on such a mass.
When you realize t h e immensevolume
you will understand t h a t a very powerful force
You can f i n d t h e s t o r y i n t h e
you wish t o examinethem,
of completely crushed rock,
must have acted on it.
It has.
huge pyramids that tower high above you.
you had better take 2 hours for the
trip.
If
If you
have t h e time, you will enjoy the geology j u s t as much as you w i l l be
annoyed by the inconvenience of passing over large, insecure
masses of t a l u s
debris.
In case you don’t have the time t o climb up there, I give you
a brief description.
About 400 f e e t above the valley, the ledges
( a n I t a l i a n name that denotes sharply fractured
and recemented rocks) end,
and about 50 f e e t above bdgin totally different rocks.
e
volcanic, but
of t h e most diverse kinds.
out that they
are i n crude layers, dipping
northwest, into the
or more thick.
i. e. millions
mountain.
of breccia
They are a l l
From the distance you can make
at about 30 degrees t o t h e
The layers and lenses are from 3 t o 10 f e e t
Some consist of solid, darkgray basalt, others are ashes,
of small volcanic fragments loosely
cemented together, but
-8-
with abundant porespaces
and cavities between.
Otherzones
consist of
m g e basaltic fragments, 1t o 5 feet across, some layered, others
some red, &hers gray
or black,
l i k e a massive plug, about
The whole assemblage forms a huge p i l e ,
a mile across.
If youworked
impressive c l i f f s , you could look across the
the south, the
sheet,about
large Ocate Mesa.
your wayup
t o these
canyon, and see before you, t o
A
l of it i s capped by one immense lava
Where did it come from? You don't see a large
100 feet thick.
volcano.
Well,
compact,,
you stand
directly
one.
A volcano, as you can see i l l u s t r a t e d on page 21 ofyour
Merit Badgebook,
has a fe6.cling channel that leads into great depths of the
e a r t h ' s c r u s t whence a l l t h e molten lava and ash came.
Mauna Loa i n the Hawaiian Islands, Lassen
which you have seen pictures, like
Peak i n g a l i f o r n i a , or VesuviusnearNaples,
e
raise the earth's surface
things, a volcanoand
Italy, are active ones.
by the expelled material.
i t s eruptions d i e some time.
old, some probablyseveralthousands
Some volcanoes have
a few eentnries
the last lava and
of years. After
volcano i s a mountain no b e t t e r or worse
than any other mountain, and as such i s subject to the remobalof
by thenever-ceasingforces
of the atmosphere:
and the sliding of loose rocks on steep surfaces.
elapsed t o remove all, or most, of
f i n a l l y be the only part
*
i t s rocks
rain, wind, f r o s t a c t i o n ,
If enough time has
t h e volcano proper, the feeding channel
of the edifice that survives.
survive for a very long time because
channel.
They
However, l i k e a l l l i v i n g
"lived", 5 . e. erupted for only a few years. Others are
ashes were blown out, an extinct
Volcanoesof
And it will, of course,
it leads t o very great depths
You can not t e l l how high the former volcanic
will
of t h e
p i l e above may havebeen
j u s t as you can not see the feeding channel of Vesuvius or Lassen Peak.
Only the one or the other part
exposed t o man.
of a volcanic center can at one time be
O u r volcanicplug,then,
tube, or perhaps a steep-walled funnel,
has aboutthe
shape of a v e r t i c a l
with a diameter of perhaps a mile.
Once t h e whole Philmont Ranch has been surveyed geologically,
we w i l l know
-9-
*
t h e dimensions much more accurately. Perhaps
b u t e t o our knowledgeof
you w i l l be able t o c o n t r i -
it, As the crushing of the wall rocks i s confined
t o t h e v i c i n i t y of the volcanic plug,
wemay
assume that the f i r s t eruption
was such a violent burst t h a t it shattered a l l rocks within a radius of
about half a mile.
The lava that i s p a r t of this plug, i s identical with the
basalt south of t h i s canyon,and
it i s almost c e r t a i n that t h i s plug is at
l e a s t one, perhaps the most important, feeding channel
by which t h e b a s a l t
was extruded t h a t flowed out as a huge s h e e t t o t h e southward, burying under
itself valleys and h i l l s of t h a t day.
before t h i s l a v a s h e e t ,
It w i l l take many thousandsofyears
too, will'have been removedby erosion.
are well advised to
When you do geological field work,you
take time out, every
you are climbing i s a
now and t h e n , ( a s t e e p h i l l
s i t down, a d t r y t o p u t t o g e t h e r all your observ-
good place t o do this!),
ations and t h e i r meaning.
A t t h i s stage, you can see tha.t
historical science in the sense
Geology i s an
that we must f i t a l l observations into a
sequence of events, or a succession of processes.
understand the meaning of scenery, the formation
Whether you wish t o
0f.a cave, or hope t o d i s -
cover an o i l f i e l d or a mining claim, the correct understanding
gradual evolution of every p a r t of the e a r t h ' s c r u s t
objective. In this respect,
of the
i s the fundamental
Geohogy d i f f e r s from aJ.1 other physical sciences.
Without t h i s guiding principle,
a l l your d i s c o v e r i e s a r e l i k e c u r i o s i t i e s
of Nature, without rhyme or reason, meaning or consequence.
One conclusion you can draw:
If t h i s plug on the north bank
of Rayado Creek fed the lava flows that spread
*
canyonmust
have formed
southward, the present
after the volcanic eruptions
had ceased.
W
e now have
several important items that allow us t o reconstruct the geological history
of thisregion.
(1) The basalt, as you saw at the start of t h i st r i p ,
north of Abreu Base Camp, l i e s above the Cretaceous Pierre shale. That
means it was eruptedlaterthantheCretaceoustime.
(2) The volcanic
just
-10-
eruptions that produced t h e g r e a t basalt mesa t o t h e south, and smaller
ones e a s t and north of you,must
quent time the erosion could
have ceased so long ago t h a t i n t h e subse-
remove the volcanic pile above the basalt plug,
and Rayado Creek could erode i t s deep notch across the basaltic rocks, into
theunderlyingCretaceous
deposited the reddish
t h e basalt plug.
red arkoses.
strata.
(3) Before theCretaceoustime,streams
shale and arkosic debris you saw before you came t o
(4) We know that there axe rocksevenolderthanthese
at the surface some distance west of
Very probably, they are
the plug, because
we have found them as boulders i n gayado Creek.
As you climb down from the steep basalt talus slopes,
pass again at the base of the gnarled gray ledges,
w h a t these rocks originally
were.
and
you naturally wonder
This has been a stiff and exerting climb.
And as you have no microscope at your disposal yet, you need again a l i t t l e
reward.
The breccia. i s t h e first outcropof
the Ranch,of
the last, oldest formation in
which you have seen the red and dark greenish-gray, crystalline
boulders i n t h e creek, and pebbles in the red arkose.
you encounter these rocks
Nowhere e l s e will
i n such a deplorably mashed and crushed conditions.
This can happen, and i f you a r e a novice, you should c o l l e c t specimens
from such rocks, take
them with you, carefully labeled and wraQped i n
paper, and keep them for future reference.
s t i l l disclose the mineral composition
A microscopicexamination would
and nature of these rocks. In fact,
i f you continue on t h e t r a i l toward Rayado Base Camp (also called Fish
Camp),you
w i l l pass these rocks for
selves much better for close study.
many miles where they lend them-
Trail from Webster Pass t o RayadoBase Camp, and on west.
m e road t o Webster Pass leads through many miles of pine
forest, which accompanies you from the low elevations at. which you start,
t o near some of the highest elevations in the Ranch area, almost 10,000
feet.
As you observe f r o m the car, the
mountains are deeply dissected,
ravines and canyon walls are well over a thousand f e e t
high,
and steep.
Between the trees, you rarely see large rock outcrops, but loose boulders
a r e much i n evidence.
This i s a common condition in the southern Rocb
Mountains, which makes geological work d i f f i c u l t .
To make a r e l i a b l e
map showing t h e d i s t r i b u t i o n of the various formations,
a
needs many w e n l y d i s t r i b u t e d outcrops.
a geologist
They need not be huge, but
they should be l a r g e and f r e s h enough t o permit him t o i d e n t i f y t h e
rocks, and secure specimens for subsequent study.
If you must map the rock formations in terrain that has only
boulders, you can not detemine the boundaries
with great accuracy because each boulder
distance from its original resting place.
and limits of the formations
may have moved downhill an unknown
Should you, therefore, locate
a boulder of quartz monzonite porphyry on a hill slope a t a known elevation
of, say, 7,320 feet, all you can say i s that this rock occurs, very
probably, a t an elevation x feet higher than
higher you can not tell.
7,320 feet; but
howmuch
If you axe i n a region of many dike rocks,
and
you f i n d a loose block of such a rock at the intersection of 2 t r a i l s , a t
i
a
a trail-stream intersection,
or any other easily identifiable point on a
slope, it would not be c o r r e c t t o show an outcrop of
point on the map.
that rock a t that
-49You will appreciate, therefore,
that the mapping of geological
-
formations at the higher elevations i n the area
distance and t e r r a i n problems
- is
a p a r t from the greater
much more d i f f i c u l t and slower than
Even with the best e f f o r t ,
i n t h e r e l a t i v e l y open low-elevation country.
the final map i s bound t o be less reliable than the one for the f l a t
Cretaceous shale areas.
i s possible, and on this
Nevertheless, progress
t r i p you will see w h a t rocks underlie most of the higher mountain slopes.
Along the half-mile or so where you walk up t o Webster Pass
from the east, youdo not pass a single rock outcrop, nor
many boulders.
do you see
But don't f a i l t o observe the material underyour
feet.
Directly as you s t a r t e d o u t from Cimarroncito Base Camp, you noted a
s
m
a
l area of gravel near the trail.
On tbis t r i p , you wlll constantly
be walking over s
m
a
l bits of rock, mineral fragments,
stones.
and small, rough
A t the moment, you do not how where this loose debris comes
from, but you make your
usual observations;
I
the fragments.
(XU out).
- (2)
(1) The commoa colors of
.
If you think you can i d e n t i f y any particular minerals
because you feel sure you have seen them before, and can recognize
specific properties or features, write them
(3) Common size, shape,anddimensions
down.
of the fragments.
-50After a short distance,
you r e a l i z e that there are about 2
or 3 different kinds of material.
Presumably, you will be i n c l i n e d t o
distinguish .&agents of individual minezals from small rock fragments,
each composed of more than one mineral species.
with w h a t you found when you walked over the slopes
you w i l l agree that the rock in these
grained than the minette shale,
of the minette hill,
Fragments is. definitely coarser-
and not a s homogeneous a s t h e brownish-gray
two principal
With a l i t t l e d i s c r i a i n a t i o n , you can recognize the
shale.
types of material, one dark and shiny, the other granular,
yellow color, and
this
If youcompare
- we may as well agree
on this one point
of pink, whitish,
- associated
with quartz.
F'rom Webster Pass, you have a f i n e view t o the south and west.
Through the ti.ees;.you can
southward, whereas
the canyon.
outcrop.
a few feet south of the trail, is your first
plenty of time,walkoverand
If youhave
go on.
look it up.
If you
You will s e e b e t t e r exposures f a r t h e r down.
Further, for your information:
The best and most interesting outcrops
are directly north andwest of RayadoBase
Camp.
half an hour t o reach the camp from Webster Pass.
your time
to the
c l i f f s of pink and reddish hues a r e on your side of
A t the pass,
a r e i n ahurry,
see the f l a t skyline of Oca&Mesa
so that youhaveenough
It w i l l take you about
So try t o economize
left; for the study of t h e c l i f f s by
the Camp.
The following information will a s s i s t you i n studying the rocks
of the RayadoCanyon
rocks.
area.
(1) There areledges of "red"rocks,
EQth rocks may appear i n one and the same outcrop.
are sufficiently coarse-grained
(2) A
l rocks
that you can, and should, observe and
a t l e a s t t h e more common minerals after a
l i t t l e practice.
and "dark"
identify
(3) The dark
-51-
e
rocks are p r a c t i c a l l y everywhere layered; the reddish rocks
may, or
may not, show layering.
The first outcrop of bedrock a t the trail is a short distance
from the pass.
Stop b r i e f l y here, and examine it.
If you can recognize layers, record,
the layers dip,
as usual, the direction in
andabout a t w h a t angle.
general orientation.
Is the rock layered?
Usecompass
which
or the sun for
If you found layers, do they dip i n t h e same
a i r e c t i o n as the Pierre shale, the
Dakota sandstone, and
the purple and
reddish sandstones you saw west of Cimarroncito Base Camp, or not?
This
as you shall see i n due time.
i s a very important matter,
Perhaps this small outcrop i s not suitable for examining and
answering all these questions.
e
But even i f i n a hurry, make it a point
t o s t o p for j u s t a moment here and t h e r e , t o assure yourself that nothing
important i n a s e r i e s of small, inconspicuousoutcrops is missed.
were new i n this region, and
If you
nobody t o l d you that a t the Camp there are
b e t t e r exposures (nobody t o l d me!),
you would c e r t a i n l y s t o p a t some length
and obtain all the data you could from even very small showings of rock.
As you now proceed along this t r a i l westward down t o Rayado
Canyon,you
will note that the small outcrops of rock, just like the rock
debris east of Webster Pass, exhibit two different kinds of rock:
dark, UsuaLly well layered,
t h e one
commonly with greenish hues, and i n some places
full of strongly reflecting scales of a mineral already known t o you and
t e s t e d a t some O%&rtrip.
Not i n every single ledge
l e a v e l i t t l e doubt about
0
Fill out the
name.
can you see it, but enough of it i s t h e r e t o
i t s identity.
The rock, however, i s not mica s c h i s t as perhaps you a r e
guessing.
If b i o t i t e mica were the only dark mineral, you might c a l l
-52-
m
it that, butassociatedwith
it i s anotherdarkmineral
but gradually t o recognize:
hornblende.
previously
in
Thesame
which you l e a r n
mineral you found
ledges
I n the
which rock:
here, youhave difficulty recognizing it because it i s intimately mixed
with mica.
However, hornblendeunderalmost
slender l i t t l e prisms, and i f youhave
surface of this rock, and
a l l conditionsdevelops
a dark, unweathered, f r e s h
you hold it in the sunlight,
you w i l l be
a b l e t o observe hundreds of
these minute needles,
the same direction,
you had drawn hundreds of p a r a l l e l s h o r t
- as if
chalk marks on a blackboard.
all pointing in about
Because hornblende makesup
a larger
volume i n this rock than mica, the rock is called hornblende schist,
or amphibole (remember from an e a r l i e r page that hornblende and amphibole
0
a r e two names from the same mineral group.
"horny substance with cleavage",and
deceiver", because
Hornblende means i n German:
amphibole, i n Greek,means
some v a r i e t i e s of this mineral deceive
"the
you easily).
Before you can observe more about the nature of this rock, you should
inspect a few outcrops of the reddish rock.
show abundant pink or flesh-colored crystals,
cleavage planes,
These, in the sunlight,
some;with excellent
and so l a r g e that you can conveniently pick out
i n d i v i d u a l c r y s t a l f r a w n t s and turn them around i n your hand.
your eyesight is a t all good,you
cleavage planes, intersecting
-
w i l l e a s i l y i d e n t i f y two systems of
a t very nearly right angles;
i f you have enough time for your examination,
perhaps,
you will recognize a
few grains that show the third, imperfectcleavage
a
If
system.
By now
you should have IIO f u r t h e r doubts that youhave again feldspar crystals
before you.Where,
the first time?
and i n which rock, did you see this mineral for
-53Closely associated with these feldspar lenses is quartz, i n individual
small grains, glassy and, a s usual, without cleavage;
whitish masses and veins.
Upon close examination, you will note a f e w
other minerals in the reddish rocks.
White or pale yellow to greenish
mica (muscovite), a l s o a coal-black mineral
prismatic shape, and
gether, like a pencil
or i n larger,
a t a very few places, of
commonly a number of these prisms are joined to-
of rays.
However, if you f a i l t o f i n d t h i s mineral
on this trip, you need not be disappointed.
Somewhere i n the western
mountains, along a trail or a creek bed, you a r e l i k e l y t o p a s s a block.
3W.s black mineral, like
qua,rtz, has no cleavage, and if you can pry
a crystal loose *om the surrounding rock,
faces, six i n nmber, Just like
a pencil.
it will show you its l a t e r a l
This is tourmaline.
RockyMountain localities, tourmaline crystals over
been found.
In some
a foot long have
On PhiSmOnt Ranch property, so far, only small crystaLs
have beenfound.
But keep your eyes open.
You may be the one t o f i n d
a larger one.
As you follow down the trail t o t h e Camp, you will note that
both the dark and the reddish outcrops remain small, say, 2-10 f e e t
across.
Try t o f i g u r e o u t their general shape, j u s t as you did with
the quartz monzodte porphyry dikes.
And do not neglect to ascertain,
from time t o time, t h e d i r e c t i o n i n which layers of these rocks dip,
and a t w h a t a m e ,
After many turns and loops, the t r a i l brings you t o Rayado
Base Camp, a t the junction of Rayado and Agua R i a creeks. After
refreshing yourself, and inspecting the luxurious
beautiful cmp, we may resum
OUT
layout of this
study of t h e l o c a l rocks.
Go t o
-54the prominent ledges,
d i r e c t l y northwest of the
C
a
m
p
, back
of the
stables, or on the north bank of Agua Fria canyon.
.If you stand about 300 f e e t upstream from the stables, where
the beaver dams a r e ponding the water of Agw R i a Creek, and look
northeast, you can make out three different
right (east), just north
of the stables,
rocks.
youhave
A t the lower
prominent reddish
ledges over a trail which l e a d s t o get p a s t the creek.
A t the lower
l e f t , you have a lagge ledge of the dark rocks you saw i n many outcrops
when you walked from Webster Pass down t o RayadoBase Camp.
And the
upper h a l f of the embankment i s occupied by a large group of dark gray
cliffs.
We may begin t o examine the lower l e f t , dark ledge.
missed the layering in the
If you
smaller outcrops by the trail, you will
certainly agree that this large ledge is well layered.
i n determining the direction
Take your time
If you
and angle of dip of the layers.
have it, look up what you recorded for the outcrops along the trail.
If you observed correctly,
agreement.
all your directions should be i n good
The layers dip a t about 4 0 t o 55 degrees to the southeast.
If you come t o another conclusion,
t r y t o d i s c u s s it with somebodywhose
eyes are geologically trained.
A
l right, i f you now stand before this ledge, and r e a l i z e that
f o r a t l e a s t a mile or so to the northeast and e a s t all the dark layers
of the amphibolite
dip t o the southeast,
you will r e a l i z e that this i s
completely a t variance with the northeasterly dip of the Cretaceous
Pierre s u e s , the Dakota sandstone,and
gray shales andsandstones
also the purplish,
green,and
that underlie the Dakota sandstone.
t h e s e s t r a t a dip uniformly to the northeast
and east.
you make another Little experiment with your hands:
A
l
Now supposing
Hold your right
-55hand so that the index finger points diagonally forward t o t h e left,
horizontally, and l e t t h e palm slope away forward t o t h e r i g h t .
you are facing north,
your r i g h t hand represents tihe Cretaceous layers
that dip a t about 35 degrees northeast.
Now hold your left hand so that
your index finger is again horizontal, pointing diagonally
right.
Ip
forward t o t h e
Turn your palm u n t i l t h e back i s sloping towards you a t about
Your l e f t hand now
45 degrees, and l e t t h e two palms touch each other.
represents the dip
of the hornblende s c M s t masses before you.You
have
a primitive model of two s e t s of s t r a t a , each many thousands of f e e t
thick, but inclined
When groups of rocks
in totally different directions.
a r e i n such a relationship, you say that they are unconformable t o
each other, or that they are separated from each other by an unconformity.
Whetheryou w i l l be able to see this unconformity anywhere
i n t h i s area, I do not how.
I 3 has not been described byany geologist
as yet, a3,though from other places in northern New Mexico such contacts
have been reported.
Once again, you can see howmuch
remains t o be done
before all the geologically important facts of this p a r t of the Rocky
Mountains will be known and carefully studied.
A t any r a t e , t r y t o
comprehend that i n the CimarronRange obviously two great blocks of
entirely different rocks are involved, the one, occupying the eastern
slopes, consisting
of a g r e a t s e r i e s of sedimentary rocks, shales,
sandstones,arkoses,conglomerates,and
so forth.
I% r e s t s , or leans,
on the high part of the range, and this, as you now can see before you,
consists of q u i t e d i f f e r e n t rocks, different in mineralogical composition,
origin, and structure.
Q
So far, l i t t l e has been said
about
red,
the
purple,
and
greenish-gray sandstones and shales
The age of the Cretaceous rocks
that underlie the Dakota sandstone.
you will i n due time be,.able t o check
by means of characteristic species of f o s s i l a
n
i
m
a
l and plant remains
for which this system is justly famous.But
the exposures of the older
p u r p l i s h s t r a t a are poor within the area of the Ranch, and no f o s s i l s
have as yet been found.
Fortunately, i n surrounding d i s t r i c t s enough
information has been gathered t o permit the conclusion
were formed during the Jurassic, Triassic,
Pennsylvanian periods. In your Merit
Permian, and possibly the
Badgebook,
find out about how long ago this was.
e
on page 2, you w i l l
You will understand that we
are dealing here with older periods in the earth's
Cretaceous.
history than the
i s that occasionally the
Now the really important thing
streams of these older periods already rolled pebbles
rocks that form the present Cimasron range.
pause t o r e f l e c t on an important matter:
that these rocks
of the same
This shoould give you
In magazinesand books of
general. information, you f i n d statements that so-and-so many million
years ago, i n a c e r t a i n p a r t of North America, there was a large volcano,
a glacier, a mountain range, or an am of the ocean.
w r i t e r s add how that i s proved.
Very rarely do t h e
But geologists must, of oourse, constantly
look a C the evidence when they t r y to reconstruct events in the history
of an area.
For this particular region,
you can say that the rocks
which form large cliffs i n f r o n t of you, and which apparently crop out
over a very large portion of these high mountains, must a l s o have stood
a t the earth's surface during these
older periods, so that streams
-57-
0
draining these slopes, picked
up pebbles, j u s t as they do now, and
finally &posited them along with the debris of red feldspar, quartz,
and much mica.
Perhaps this w i l l impress you, perhaps it won‘t.
any r a t e , you should r&.ize
At
that we can make some very positive and
reliable statements about certain things.
When you keep i n mind that
geological time i s measured i n m i l l i o n s of years, not just centuries
or millenniums, l i k e human history, you will a t least a W t tha%
we
a r e concerned here with times as remote compared with human history
a s is the space of the gaLaxy i n comparison with the space of our
solar system.
Some of us need a special stimulus t o become enthusiastic
If you need one, consider this:
aboutsuchthings.
a
are not in these
but you
have
Supposing you
mountains to piece together a certain geological story,
been hired by amining
company t o explore this area econo-
mically, l e t u s say for metallic ore deposits, such
molybdenum, niobium, t i n , or copper.
conglomerates, and
as tungsten, cerium,
You would then e d n e the reddish
i f you f i n d among the pebbles some that contain these
metallic minerals, you would a t once d r a w an important conclusion
which rocks may contain deposits of these metals?
as to
When you keep i n
mind that it may take a day or more t o map one single square mile
t h i s mountainous t e r r a i n , you can figure out how muchmore
of
effectively
your exploration will proceed i f you know i n advance that only one
group of rocks, but not any other, i s l i k e l y to contain the deposits
wish to locate. Alertness in
l
e,
that nearly every discovery
you
making geologic deductions, and an awareness
i n “pure Science” has its d i r e c t commercial.
applications will convince you that it pays t o work out careW1y these
larger relationships between individual. formations.
!
-5&
I
Cimarron and Sangre de
As a matter of fact, the present
Cristo Ranges seem t o have been a t l e a s t as large and as high as
they are now.
If you drive on U. S. ighway No.
64 from EagleNest
t o Taos, you pass for over 12 miles some of the same s t r a t a on the
west slope of the range.
-
Here they are not
as coarse as some of the
conglomerates i n Philmont, but there are thousands of f e e t of them,
and if you stop often enough,you
can c o l l e c t many well preserved
f o s s i l s i n t h e s e sandstones and shales.
The range therefore m u s t
have been a highland that provided the streams of that time with all
the debris t o buiM up l a r g e p i l e s of sedimentaround it.
mountain range
a t the present time acts
in the sameway
Every
as a source
area for stream &bris.
e
The picture of a high mountain range that stood here back
aslong
ago as the Pennsylvanian
period,
i s only
a
into the geologic past of this p a r t of New Mexico.
momentary glimpse
It would be wrong
t o assume that t h e CimarronRange has been a mountain range ever since
the Pennsylvanianperiod.
Some time a f t e r t h e Pennsylvanian streams
flowed off this range, the land probably sank, and quite a d i f f e r e n t
sceneryfollowed.
But we a r e g e t t i n g ahead of ourstory.Let
to the ledges In f r o n t of
us.
us r e t u r n
Before us a r e s t i l l the ledges of amphibolite and the red rocks.
It is time now t o f i n d o u t something about their origin and nature.
Geologists long before your time
amphibolites.
e
have t r i e d t o o b t a i n f o s s i l s from
They a r e so well layered they suggest sedimentary rocks.
The layers appear quite undisturbed, and f o s s i l shells might therefore
be preserved.
A
l these attempts have failed.
It is the same with
mica schist, and i n some of the dark ledgesinFria
Canyon there
-59i s so l i t t l e hornblende that the rock could be called a mica schist.
If a geologist finds a f o s s i l i n mica schist, he writes forthwith
a r t i c l e announcing this remarkable fact.
89
He publishes a photopaph
of it, and his f r i e n d s a r e l i k e l y t o drop i n on him t o see the remarkable
find.
Yet mica s c h i s t and amphibolites underlie many thousands of square
miles i n every continent.
It has taken geologists a long time before they figured out
just why these rocks lack fossils.
that produce, say,
If we can observe the conditions
a cubic yard of dune sand, or a ton of mud or gravel,
we can pretty well understand how these rocks have formed on a l a r g e r
scale in nature.
However, no mica s c h i s t or hornblende s c h i s t has y e t
formed under the eyes of human beings, and
cessfully produced theserocks.
no experiment has yet suc-
There arereasons for this.
Nearly
all the rocks you see are composed of minerals i n w h i c h s i l i c a , or
the oxide of the element s i l i c o n (SiOZ), i s the most important single
cons6ituent.
(chis oxide, when pure, appears as quartz, and you have
seen it i n many pbces.
form morecomplex
But as s i l i c a combines with other elements t o
s i l i c a t e s , it imparts t o them the unpleasant property
of requiring very hi& temperatures t o form crystals.
Furthermore,
most of these crystals grow extremely slowly, and some have, so far,
refused t o form any c r y s t a l s under laboratory conditions.
You need not go i n t o all t h i s detail, but two things a r e
worth remembering:
(1) Nearly all the minerals in the rock before
you require temperatures above t h e b o i l i n g p o i n t of water t o form:
(2) Rocks, l i k e mica s c h i s t andhornblende
schist, do not form where
volcanic lava has acted on ordinary surface rocks, although
a rock like
-60-
a
the Cretaceous hornfels,
west of Cimarroncito Camp, has some minerals
i n common with hornblende s c h i s t and mica schist.
Many s c h i s t s and amphibolites have been chemically analyzed,
and it i s known that a mica s c h i s t has the same chemical composition
(and a l s o t h e same layered structure) as mud and shale.
There is very
good evidence t o show that if a shale will be brought i n t o r e l a t i v e l y
deep l e v e l s of the earth's crust, say, 4 or 5 miles below the surface,
it will be under
sufficient heat and compression t o start growing
mica flakes; and if the shale had a c e r t a i n amount of lime, it will
developboth mica andamphibole
crystals.
Our hornblende s c h i s t and
mica s c h i s t have almost c e r t a i n l y gone through such a process, and
rocks of this kind are spokenof
i n Greek,means
fabric.
as "metamorphosed rocks".
"of changed shape", and
Metamorphosed,
r e f e r s t o t h e changed c r y s t a l
The formerly powdery, fine-grained m u d or shale i s now composed
of large enough flakes of mica so you can reco@ize
You will understand, then,
individual crystals.
that t h e frail s h e l l s of bivalves
or other fossils a r e n o t l i k e l y t o p r e s e r v e t h e i r shape if the e n t i r e
substance of the rock has been so thoroughLy changed.
This i s thought
t o be the main reason why f o s s i l s i n metamorphosed rocks are excessively
rare.
Yet a few have been found i n various parts of the world, and they
prove that many metamorphosed rocks are of the same, or of younger age
than ordinary unmetamorphosed sedimentaryrocks.
thought that d l metamorphosed rocks are very old.
in recent years.
not so old.
Some time ago, it was
T h i s has been disproved
A good many metamorphosed rocks are old, but others are
The matter must be examined i n each region,
i t s own evidence.
and juQed
on
-61-
e
So much for the dark s c h ifisnrto n t
As you walk
of you.
on, up Agua Fria Canyon, you will pass manymore ledges of it, all
dipping a t intermediate angles to the southeast,
and you will r e a l i z e
that this i s a huge system of s t e e p l y t i l t e d metamorphosed sedimentary
rocks.
How old are they?
always give a direct
man on the street.
To this question a geologist can not
answer, j u s t as you can not i f youmeet an unlmown
But you canuse
some
common
sense.
The man c e r t a i n l y
i s not a baby any more because he walks on his own legs:
and he walks
along q u i t e b r i s k l y so he i s probably not yet over seventy.
the same reasoning whenwe
W
e apply
try t o figure out the age of a new rock.
We may not bow i t s exact age, but may h o w that it i s younger or
e
older than some other rocks whose age we doknow.
Do a l i t t l e t h i a n g ,
then, and write down your best guess.
Now
we
come
t o t h e r e d rock, i n f r o n t on your right.
have been s t a r i n g a t this cliff f o r so long a time,
t o examine it.
we should be off
But it may be as well t o s t a y a t the observation point
for another minute, because
The rock itself,
the s t o r y of the red rock i s not so simple.
as you have found out by now, is a rather coarse-grained
aggregate of pink and yellowish feldspar crystals,
with much less quartz
i n i r r e g u l a r g r a i n s o r larger masses, plus still l e s s
vite or the
W
e
dark b i o t i t e .
mica,
e i t h e r mtzsco-
Rocks having this mineral composition,
may be
called granite although, when the grains are as coarse as they are in
ledge, most g e o l o g i s t s c a l l them pegmatite.
Don't worry about t h a t name.
It is derived from a Greek gadget used on the stage, but
i n t o all this.
our
we need not go
-62-
e
Now as you
examine
the
ledges,
or fine-grained,appears
rock,
whether
coarse-
for instance, i n t h e cliffs on your l e f t .
hornblende schist.
monzonite porphyry,
as
red
l e n s e si n
and
You can also see true dikes of the pink rock,
between t h e amphibolite.
of the
th
th
ae
t
you w ifliln d
They break across the layers
Remembering your experience with the quartz
you will consider them volcanic rocks,
and about 1.50
years ago, it was assumed that i f all volcanoes of the e a r t h had been
visited, and their eruptions and lava studied,
that erupted granite lava.
some would be discovered
But there are none that
that there probably never were any that did.
do, and wenowknow
Instead, many volcanoes
have been found that produce a lava that resembles g a u i t e i n composition,
but nowhere are such volcanic eruptions actually connected with masses
e
of g a n i t e .
An enormous
The two rocks carefully avoideachother.
amount of work has been expended during the last 100 years to solve this
r i d d l e of the granite.
It is, however, so complex that t o this day the
complete answer i s not known.
For the rocks in PhiUnontRanch,you
followingobservations:
(1) Theirmineralcomposition
where the same, and q u i t e simple;
a r e massiverocks.
can and should make the
i s nearly every-
(2) The majorityofthegraniteoutcrops
-
If they are layered, the layers
conform t o the l a y e r s
of nearby schist and amphibolite; (3) Occasionally, s t r i n g e r s and dike-like
offshoots extend from a granite or pegmatite lens across the dask rocks,
and i n some dark rocks you f i n d t h i n films, nests, and quite irregularly
shaped bodies of the pink rock.
compact, or faintly layered;
(4)
They may be coarse-grained, medium-grained,
~n
some outcrops, you can not draw sharp
-63boundaries between the red and dark rock.
pinkish feldspar grains are scattered through the
proportions and without sharp boundaries.
or
Instead, the white
dark rock i n all
When you stand in front
of a t r u e dike of granite that cuts across the layers
of schist, you
can hardly f a i l t o assume that the granite was something like a liquid
that was forced into a f i s s u r e of the dark rock, and pried the walls
apart, an inch here,
Tlzis i n t e r p r e t a t i o n is still
maybe more there.
favored by many geologists, and outcrops like these justify the belief
that a t l e a s t some granite i s a liquid, deep i n the c r u s t of the earth,
that will rush into any available spaces of the surrounding rocks.
However, as you read before, liquid granite has never been observed
t o flow out a t the surface of the earth.
other rocks, but falls to extrude
-
As it seems t o break into
a t the earth's surface,
when solidified, i s called an "intrusive" rock,whereas
that does break through the crust,
such material,
volcanic lava
i s cailed an "extrusiv&'
rock.
These somewhat lengthy comments have been given here because
the study of metamorphosed and intrusive rocks i s muchmore
than that of ordinary sedimentary and volcanic rocks.
one ledge t o another, and
of granite, pegmatite,
difficult
As you walk from
pass the endless succession of irre@;ular masses
or mixed rocks, on the canyon slopes you will
remember the contrast between the simple layers of t h e P i e r r e s W e ,
the purplish sandstone, or the gray Dakota sandstone, and
these meta-
morphosed rocks, complex i n o r i g i n and v a r i a b l e i n composition and texture.
I n this part of New Mexico,however,
the amphibolites, schists,
v a r i e t i e s a r e t h e most ancient rocks.
They underlie the cores
and granite
of the
-64as a
Sangre de Cristo, Cimarron, andTruchasranges,andcontinue
huge complex
i n the Front Range of Colorado.
Many striking mineral
l o c a l i t i e s and many deposits of economically important metal. m2nerals
have been found i n t h e s e rocks, though not within the area of
Philmont
Ranch.
3LT you have examined the many ledges of the
dark, schistose
amphibolite, and the numberous lenses and s t r i n g e r s of red granite,
i f youhave
and
some s t r e n g t h l e f t , you can examine the third ledge you
saw from yourobservationpoint
a t the beaver dams.
Remember:
the
top of t h e c l i f f n o r t h of them looks quite different f r o m the metaA b r i e f visit t o that ledge i s well mirth
morphosed rocks underneath.
while.
You climb t o t h e t o p of the red granite-pegmatite,
red color of the loose blocks
ceases.
and the
M y grayones l i e around, some
firm, others full of holes and pore spaces.
If you have previously
walked along the trail from AbreuBase Camp t o Rayado Canyon, end
studied the great volcanic
Psug on the north side, you w
l
l
if e e l l i k e
a veteran from the WorLd W a r who condescends t o take a shot gun and
shoot a squirrel.
A t any rate, yow geologically trained eyes
will
spot a t once t h e t e x t u r e and firm composition of this gray rock as
t y p i c a l of t h e b a s a l t that underlies Ocate) Mesa, south across the Agva
Fria Canyon.
R i g h t you are.
This i s basalt.
the cliff. Is it a l l firm basal.t? -st,
Now walk t o t h e base of
butnotquite.
If you
walk slowly around the base of t h e c l i f f , you will f i n d a Pew small
showings of basalt-tuff.
A tuff i s volcanic ash, cemented together.
Some forms a firm, strong rock, some i s so full of gas c a v i t i e s that
it i s l i t t l e more than loose bits of rock.
of the l a v a c l i f f s l o p e a t
v e r i f y this.
The tuff lenses a t the base
about 30 degreesnorthwest.
Never believe anything without
To that exten+,,
(You had b e t t e r
first checking up on i t . )
they do the same a s the ash and tuff layers a t the
south base of the large plug, west
of AbreuBase Camp.
t h e r e s t of t h e c l i f f i s a muchmore
modest affair.
But obviously,
If youhave time,
walk on north, always along the eastern base of t h e b a s a l t c l i f f .
going i s a b i t slow, b u t a f t e r some
the ledge.
300 f e e t you come t o t h e end of
While you a r e up there, take
Creek to the northeast.
The
a good look across Rayah
There a r e some interesting-looking outcrops,
a t exactly the same elevation as the base ofyour
Do
basalt cliff.
n o t h e s i t a t e t o go up there i f there is time.
You can r e t r a c e your steps, following the basalt leages
t o t h e n o r t h bank of Agua F’ria Canyon, and as youdo,you
back
will r e a l i z e
that this mass of b a s a l t i s quite small, perhaps 400 f e e t o r so from
west t o east.
If you were a t t h e l a r g e plug, you will r e c a l l t h e i n -
teresting speculation wemade
t h e r e i n r e g a r d t o t h e age of the basalt,
and how old or how recent Rayado Creek might be.
place here involves the
same problem.
immense mass of mesa basalt.
as the base of
Hereyou
You can see that t h i s
Across the canyon,youhave
the
stand a t about the same l e v e l
that mesa, b u t i n between i s that deep ravine.
How do
you explain it?
The tuff a t the base of our b a s a l t c l i f f maymean
that the
first eruption started as an explosion of ash, and then a Barge b a s a l t
flow followed and buried it.
But it i s probably not necessary
t o assume
-66-
8
that this b a s a lct l i f f
or feeding channel of the
i s another
plug
basalt extrusions. Certainly the red granite
and dark amphibolite
ledges underneath show nothing comparable t o t h e extreme crushing
you saw at the base of the large basalt plug.
As you inspect the basalt ledge
n o t i c e v e r t i c a l columns.
that faces the stream, you
Basalt all overtheworld
shows this.
The
columns t e n d t o p o i n t a t right angles to a surface that cooled the
b a s a l t when it erupted.Therefore,
f l a t cooling surface; horizontal
surface.
v e r t i c a l columns form above a
columns demand a vertical cooling
'R.y t o f i g u r e o u t w h a t kind of a shape(and
name for it!)
a mass of b a s a l t must have t o show horizontal columns.
A familiar analogue of columnar basalt is cracked
e
puddle.%re,too,
surface.
there i s a
-
md i n a dried-up
the mud columns a r e a t r i g h t angles to the cooling
Both features have i n common that %he substance has shrunken.
The mud l o s e s i t s water; the cooling basalt lava loses a large
volume
of associated gas and steam.
As you walk back from RayadoBase Camp t o Webster Pass, you
will notice by t h e t r a i l q u i t e a few blocks of basaltic lava.
have extra time, climb up, some 400 f e e t a f t e r l e a v i n g t h e
will f i n d more c l i f f s of volcanic rocks there,
t o determine the shape of these masses.
If you
camp.You
and may f i n d it i n t e r e s t i n g
- Ponder another point:
If the
b a s a l t c l i f f on the north bank of Agws Fria Canyon is not a remnant of
a feeding channel, how did t h e b a s u t g e t t h e r e ?
* .
TRAIL FROM RAYADO (FISH)CAMP TO ABREU BASE CAMP
-67-
This section of the trail gives a typical picture of the principa1
types of crystalline rocks that underlie the core of the Cimarron Range.
The trail, accompanying the creek, follows a southeasterly direction,
whereas all the layered rocks strike northeast-southwest (or n e a r l y so).
Thus the trail is a t r u e c r o s s - s e c t i o n , a c r o s s t h e s t r i k e of the bedrock
formations.
As elsewhere in t h e c r y s t a l l i n e r o c k s of the Cimarron Range,
two principal rock types make their appearance: (1) Dark greenish-gray
amphibolites (or hornblende schists), and (2) pink or light gray granite
(in places layered, or foliated), blending commonly into the coarse-grained
'*
v a r i e t i e s known as pegmatite. These
two rocks constitute, for the most
p a r t , a great system of p a r a l l e l l a y e r s a n d l e n s e s . T h e r e a r e p r a c t i c a l l y
no complications, and both structure and mineral composition of t h e r o c k s
are easily learned.
The first ledge, about 1,000 feet southeast of Rayado Camp, on the
southwest side of the trail, shows well layered, typical amphibolite, with
l a y e r s dipping at about 25 d e g r e e s s o u t h . S o m e l a y e r s a r e d a r k e r a n d
coarser than others.
This is due to more amphibole (or hornblende4 both
terms denote the same dark greenish to black, prismatic mineral) and less
of the light-colored minerals quartz,
and white mica (muscovite). Two
pink to maroon pegmatite lenses, 1-2 f e e t t h i c k , a r e p a r a l l e l t o t h e
*
amphibolite layers.
is slightly folded.
This is almost the only ledge in which the amphibolite
-68-
About 300 feet southeast, in the trail, the amphibolite layers dip at
about 45 degrees southeast, and are accompanied on the northwest by a l a r g e
pegmatite mass, p a r t l y in the creek bed. Prominent joints dip
at about 60
it might be well to
degrees northeast. Here and in subsequent outcrops,
point out the great importance of f r a c t u r e s i n r o c k s f o r the circulation of
ground water and other solutions in the earth's surface.
The rocks in this ledge continue across the creek ina large cliff.
"Last Mile Bridge". On the left
(NE) s i d e of t h e c r e e k is a large ledge of
pink pegmatite, accompanying amphibolite, some layers
of which a r e r o t t e n
and brown, due to oxidation of the iron compounds in the hornblende and black
e
mica (biotite). The pegmatite
is conveniently located f o r a study o f i t s
principal minerals, and their identification. Nearly
all the pegmatites in
t h i s a r e a h a v e two v a r i e t i e s of feldspar: the pink potash feldspar, or
orthoclase, and the white soda-lime feldspar,. o r plagioclase. Occasionally,
the pink feldspar in pegmatites shows wavy, white or grayish, thin zones. This
v a r i e t y is k n o w n by a special name, perthite. The thin wavy zones are very
thin plates andfilms of plagioclase within the more voluminous orthoclase.
It is generally thought that when these crystals originally formed, they were
homogeneous. But upon cooling, the two different types
into these thin f i l m s .
of m o l e c u l e s s e p a r a t e d
It can also happen that white feldspar is the potash-bearing
variety, but where pink feldspar is present, the white one is nearly always
.I)
'
plagioclase.
Gross gate in wire fence.Above
it, on the north
side of the
canyon, a r e l a r g e p e g m a t i t e cliffs.
They are steeply dipping lenticular
masses t h a t r e a c h n e a r l y all the way up the slope.
150 feet southeast, the trail crosses over to the southwest side of
the creek.
Soon afterwards, the north bank exposes large plates of d a r k
gray amphibolite, dipping at 60-70 degrees southeast. This
is a v e r y
characteristic view of the structure of the amphibolite formation in this
entire canyon area. Each layer,
1 or more feet thick, can be followed
along its c o u r s e f o r o v e r 100 feet. Note that these layers
not folded,
are m e r e l y tilted
If folds were present, one would almost certainly see the places
( a p i c e s ) w h e r e t h e l a y e r s b e n d a r o u n the
d axis. T h e r e are apparently no
such places anywhere around.
After an i n t e r v a l of about 1,000 feet where thetrail runs over talus
d e b r i s , it s k i r t s a steep ledge of pegmatite on the south bank of the creek.
H e r e the r o c k is l a y e r e d i n p l a c e s . T h e l a y e r s d i p at about 30 d e g r e e s t o
the southwest. At the southeast end
of this ledge, the trail c r o s s e s o v e r t o
the north bank. The pegmatite continues here, and shows many large feldspar
crystals. The reflecting cleavage surfaces reach the size
of a man’s palm.
At the f o r d , t h e r e is a light gray quartzose lens in the pegmatite. Just
possibly this is a small mass of a former sandstone, metamorphosed to
quartzite, and so thoroughly soaked by the pegmatite that some feldspar got
into it.
The rock might be called
a quartzose gneiss. This rock continues
-70-
f o r s o m e 120 feet downstream on the north bank. The rock shows well
developed layers, and they dip in the usual direction, to the southeast,
at about 75 degrees. The
resistant r o c k m a k e s a prominent reef in Rayado
Creek. Note also the sharp fractures. Nearly
all brittle rocks have them.
F a r t h e r s o u t h e a s t , t h e q u a r t z o s e g n e i s s is i n t e r l a y e r e d with d a r k ,
thin amphibolite layers, and this rock increase.sin volume farther southeast.
At one place, where the trail skirts the steep northern front of a prominent
ledge, many loose slabs of amphibolite show nicely the individual hornblende
c r y s t a l s , as black thin needles., about 1/8-inch long. They show best in
light-colored, muscovite-rich blocks, and here and there, the hornblende
e
needles are concentrated in little r a d i a t i n g c l u s t e r s , s e t in the white,
glistening micaceous base.
The trail c r o s s e s a n d r e c r o s s e s t h e c r e e k at s h o r t i n t e r v a l s now.
Near the east end of this l a r g e g r o u p of steep ledges is a beaver dam
(incomplete as yet), and the creek makes a sharp right-angle curve, turning
f r o m e a s t t o s o u t h . At the knee of the stream, fine-grained pink gneiss dips
at about 30 degrees south.
Again, the trail c r o s s e s t h e s t r e a m at short intervals because so
many steep cliffs are crowded togethernow that there is not m u c h r o o m f o r
the trail.
*
Many of these ledges display typical, coarsely crystalline
pegmatites, and it is impossible to overlook the many large cleavage fragments
of feldspar. It will be noted that all larger cleavage surfaces are composed
of individual, small surfaces that have nearly, but not quite, the same
orientation. Such "mosaics" are the normal thing in rocks that have gone
-7 1-
through deformation and uplift. The originally large and uniform crystals
have been strained, not quite enough to rupture each crystal, but enough to
dislocate nearly every individual internally. The microscope shows that
these small dislocations go to much smaller dimensions.
Farther east, amphibolite reappears, striking northeast, but dipping
to the southeast as well as to the northwest, and near the eastern end of
the tract, the rock becomes massive and somewhat coarser-grained, with
many small pink crystals, probably orthoclase.
r” to the Scouts what an amphibolite
At this point, it m a y be well to explan
is. Chemically, these rocks agree closely
e
lava, but also with that
[I
with the composition of basalt
of calcareous shales.
In other words, where rocks
have been metamorphosed (and all amphibolites are metamorphosed rocks),
two r o c k s of entirely different origin can give rise to the same metamorphosed
rock..
It is always desirable in geology to ascertain the origin of rocks. This
ledge of massiv? amphibolite helps.
layered rock. Although the process
A calcareous shale is a sedimentary, i. e.
of metamorphism replaces the original
m i n e r a l s of the sediment with another mineral association, .it r a r e l y c a n do
away entirely with the layered structure
of a sedimentary rock.
A massive
amphibolite, therefore, is suggestive evidence that the rock was not
rock to begin with, but a basaltic one. Although some basalt lava
*
layered, this is the exception, and not the rule.
a sedimentary
is also
On ihe highway (U. S. Highway
64), west of t h e P a l i s a d e s of t h e C i m a r r o n , t h e r e a r e m a n y f i n e o u t c r o p s
showing amphibolites grading into fine-grained basalt that has only slightly
been metamprphosed. Therefore, there are
2 l i n e s of evidence for the basaltic
-72-
origin of these particular amphibolites. Well layered amphibolites can
also be of basaltic origin, in the sense that they may represent metamorphosed
-
basalt ash, ortuff, which is commonly layered.
At the east end of the massive amphibolite, many pink granite
lenses penetrate the rock, which here becomes again better foliated, or
layered. The
trail now crosse's over to the south side
of the stream, and
c l i m b s o v e r a l a r g e m a s s of pegmatite, with pink and white feldspar, and
a more generous admixture of white mica (muscovite) than is common here.
Biotite and quartz are also present.
At the east end of this pegmatite promontory is an obsolete shelter
e
on the right side
of the creek. About
80 feet southeast of the shelter,
on
.
the right bank of Rayado Creek, the southern contact of the pegmatite mass
is exposed. The surface dips
at about 55 degrees north and the pegmatite
r e s t s on fine-grained feldspathic gneiss that has the regional southeasterly
dip.
Its l a y e r s a r e c u t
off by the contact. Directly opposite the shelter,
on the northeast side of the creek, is a white quartz vein of irregular shape
in the pegmatite ledge.
The trail c r o s s e s on a wooden log bridge over to the north bank of
the creek, and pegmatite with much muscovite continues there. Pink finegrained gneiss is exposed east of the pegmatite. Some
100 f e e t e a s t , on the
north bank of the creek, and directly by the trail, can be seen the floor contact
-73-
of an irregularly shaped pegmatite, which rests onthe fine-grained gneiss.
300 feet east, the trail c r o s s e s to the south side at a steep rocky
gorge. Pegmatite
i s again the most prominent country rock,
and about
Z O O feet east, on the north bank, is a steep tan-colored pyramid of pegmatite
and fine-grained gneiss, nearly ZOO feet high. Only loose blocks are on the
south side where the trail goes; but about 150 f e e t farther east, pink finegrained quartzose gneissis passed in the trail.
About 4 0 feet downstream, the trail crosses over to the north bank.
Yellow, rotten gneiss,
e
with amphibolite zones, strikes northeast-southwest
here, dipping at about 75 degrees southeast. The amphibolite from here on
east looks crushed, and chunks of it appear in twisted position in the pegmatite.
T h i s is the last outcrop in whichthe crystalline rocks exhibit their
normal features.
On the north bank, east of here, appears the west end of
the huge talus pile that strews the southern slopes of the great volcanic plug,
which culminates in the two spectacular pyramids of brick-red color. Several
outcrops of t h e c r y s t a l l i n e r o c k s a r e p a s s e d just n o r t h of the trail, and despite
the immense cliff surfaces it will be very difficult for anyone to recognize
the familiar amphibolite, fine-grained gneiss,
o r pegmatite.
All r o c k s h a v e
been crushed by the force of the volcanic eruptions that blew the lava and ash
through the crust of the earth, and every single ledge is shattered by thousands
of cracks, even though the rocks hold together fai?ly well. In a few of t h e s e
-74-
.
i
brecciated
cliffs,
however,
coarse-grained,
massive
hornblende
rocks
a r e still identifiable, but their relationship to the surrounding granitic
r o c k s is effectively obscured by the crushing andthe staining of all crack
surfaces with iron oxides, silica, or other coatings of fine-grained
cementing material.
Robert Balk, Economic Geologist
New Mexico Bureau of Mines and M i n e r a l R e s o u r c e s
Socorro, New Mexico
June 2 , 1953