GEOLOGY OF THE NORTHEAST CORNER OF
THE SPARTA QUADRANGLE AND
VICiNITY, OREGON
by
FRANK FELLOES GREENE
A THESIS
submitted to
OREGON STATE COLLEGE
In partia' fulfillment of
the requirements for the
degree of
MASTER OF SCIENCE
Fh
It1
APPROVED:
Redacted for privacy
1
----
Associate Professor of Geology
-In Charge of Major
Redacted for privacy
Chairman of Department of Geology
Redacted for privacy
Chairman of School Graduate Colttee
Redacted for privacy
Dean of Graduate School
Date thesis Is presented March ii i96
Typed by Juan I ta R. Greene
ACKNOWLEDGMENTS
The writer wishes to express sincerest appreciation to
his major professor3 Dr. William
assistance
. Taubeneck, for his guidance,
nd constant encouragement In the preparation of this
thesis.
Thanks are also extended to Mr. 0. 0. Cochran and
Mr. J. C. Cummings for their helpful suggestions concerning
structural problems, to Dr. D. A. øostwick for interest and
advIce on paleontological problems and to Ors. Ira S. Allison
and W. 0. Wilkinson for reading and offering helpful suggestions
regardIng the final preparation of this manuscript.
The writer Is also Indebted to Dr. S. W. Muller for
identificatIon of fossils, to Mr.
1I11an W. Woods for general
mining Information, and to Mr. R. Q. Lewis for interest and
assIstance In gaining information from the records of the U. S.
Geological Survey.
Lastly, I would like to express my sincerest thanks to
my wife, Juanita, for her persistent encouragement, understanding,
and assistance, for her critical reading and editing of the rough
draft, and for typing of thIs final manuscript.
TABLE OF CONTENTS
Page
INTRODUCTION.
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Purpose of investIgation
Location and accessibIlity
Field and laboratory rk,
Previous rk. .
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GEOGRAPHY
Physiography
Drainage
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Climate
Vegetation
GEOLOGY .
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Stratigraphy
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ID
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10
CloverCreekgreenstone . .4.4..... * ****ø 11
Distribution and topographic expressIon. . . . .
U
Lithology and structural features. . . . . . . . . 12
Petrography.
14
S reenschist. . , .
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ilornblende liornfcls.
17
Special study metamorphosed amygdules. . . . . 20
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Deposlticmalenvronment............'.Z3
Age
and stratigraphic relations.
24
Albite granite
24
Distribution and topographic expression. . . .
. 25
Lithology
a
Texture.
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ComposItion.
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Paragenesls.
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Normal crystallIzation
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Texture.
CoITposition.
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Pie tamorphism
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Dispersal. . . . . . . . * . . . . .
Depositlonal environment . . . . * .
Provenance .
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Age and stratigraphic relations.
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Age and stratigraphic relatIons. . . . . . .
Lower Sedimentary series
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Distribution and topographic expression. .
Lithology and structural features. . . * . .
Petrography. . . .
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* 33
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34
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Albitization and siUciflcatlon.
Regional metamorphism.
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and structural features.
Pet rography.
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45
45
48
4$
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a
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51
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Martin Bridge formation , e a
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Distribution and topographic expression .
Lithology and structural features . . a
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Petrography a a a a a a
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Texture .
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Mineralogical composition a a a a a a
Chemical composition. . a . a a
a
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Depositlonal environment. a a a a a a a .
a
a
Age and stratigraphic relations a a
a
Hurwal formation. . . a . a a a a a a
a a
Distribution and topographic expression a
Lithology and structural features a a a .
a
Petrography a a a a a a a
a
a a
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Texture a a a a a
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Coios1tion a
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Deposltional environment. . a a a a a a a
Age and stratigraphic relations a a . a a
Columbia River basalt . . . . . . . . . . . .
Distribution and topographic expression a
Lithology and structural features a . a a
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Conditions of deposition. a a . a a a a a a a a
Stratigraphic relations and age a a a a a a a
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Unconsolidated deposits a a .
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Terrace deposits. . a a a a a a a a
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Alluvium. a a a a a . a a
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Structure a . . a a
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Post"Permian1 Pre..
r Triassic deformation. . a a
Post-Triassic, PreaaCretaceous deformation a a a a
Early Cretaceous deformation. a a a a a a .
a
a
Post-Middle Miocene, PresPleistoceno deformation. a
Dome-Like structure a a a a a a a a a a -e a a a a a
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-Petrography a
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Texture .
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Coniposl tion a
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Mlnlnggeology. a
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History .
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Description and production of mines
Historical geology. . a a a a a a
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BIBLIOGRAPHY a
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.104
FIGURES
1.
indexmapof Oregon.
P age
... 5
sea..,.., ....
.
6
. . . .
12
2a. Microscopic Illustrations of greenstone textures . . . . . .
15
2. Greenstoneoutcrop . .
. .......... ... .
3.
Photom1crogrh of metaorphosed anygdule.
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4.
AlbIte granIte outcrop
a
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5.
Outcrop of Lower Sedimentary series.
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a
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S
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6. Graded bedding in Lower Sedimentary series graywacke
7.
Martin
Bridge
limestone outcrop.
.
a
a
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8. Fold structure In Martin Bridge
formation,
a
.
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a
a
a
9. Cnchodon sp. cf. £. knfratiasicus
'
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e
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42
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22
26
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10,
Copchodon sp, cf, £. Infraflasicui $toøn1.
11.
Coli,unbla River basalt.
.
a
12.
Spheroidal weathering of Columbia River basalt
a
13.
Frequency dIstribution curves for unconsolidated deposits'
a
81
14,
Index map showing mining locations and distributIon'
.
97
15.
Trn basaltic feeder dikes
16.
GeologIc map and sections
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102
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108
TABLES
I. Eaglecreekwaterdlscharge... .
Z.
Cflmetological data
3.
GeneralIzed section of rock formations
.
4. Modes of albite granite.
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''
'
e
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10
a
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8** .......
Modes of Lower Sedimentary series graywacke.
6.
Analysesof limestone.'
7.
Modes of typical Columbia River basalts'
8.
Data of mines and prospects.
a
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5.
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Page
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* 74
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94
GEOLOGY OF THE NORThEAST CORNER OF THE SPARTA (UADRA$GLE
AND VICINITY, OREGON
INTRODUCTION
Purpose of investigation
Th. purpose of this thesis Is to contribute to knowledge concern*
ing the geologic evolution of northeastern Oregon.
This thesis presents results 0f geologic mapping and laboratory
study of data and materials
collected In an area of approxImately 50
square miles In the southern part of the Wallowa Hountains and is one
of several theses at Oregon State College synthesizing geologIc reia-'
tions in this region.
Location and Accessibility
The thesis area is located In the northeastern corner of the
Sparta quadrangle and Includes a small portion of the northwest corner
of the Halfway quadrangle.
the
440551J5fl
More specifically, the area Is bounded by
and the 45° OO'OO" north latitudes and the 11701330u and
the 1,7024100 west longitudes.
Accessibility is provided by numerous forest service, logging,
and mining roads, most of which are serviceable to conventional automobile travel during the sumeer season4
Forest trails, livestock
driveways, and old water ditches facilItate foot travel In sections not
traversed by roads.
The principal automobile routes to the area Include Eagle Drive,
a well serviced road entering from the southwest and following Eagle
Creek to the northwest; SIt Cabin road, a poorly serviced route
entering from the east and connecting with
Eagle Drive near Martin
Bridge; and the Little eagle road, a very rough and undependable route
entering the southeastern corner of the area from the town of R.Ichland
and connecting with the Suirn1t Cabin road at Snow Fork Creek.
The
recoawnended route to and from the area Is Eagle Drive which connects
with State Highway 86, approxImately 1.2 mIles east of Colvards
store
and 23 ml Jes east of Baker, Oregon.
Field and Laboratory tIork
Field studies requIred sixteen weeks during the sunwaers of 1958
and 1959.
Geologic control during the first field season was limited to
the accuracy of the U.S.G.S. Pine quadrangle and to aerial phctographs
where this map was in error.
Location of Jithologic contacts and
other points of geo1og1c1 significance were established by use of the
Brunton Pocket Transit and Engineers Barometer.
During the latter
part of 1958 the U. S. Geological Survey released advanced (15-minute)
sheets of the Sparta
nd Halfway quadrangles which covered the area
formerly included In the Pine quadrangle.
The second season wee con-
fined primarily to transfer of Information to these later maps and to
restudy and rechecking of certain doubtful areas.
Laboratory studies include insoluble residues, partial chemical
analyses, grain-size analyses, statistical coaputations of lithological
and structural data, and
microscopic examination of 165 thin sections.
Previous Work
Literature dealing witn the geography, geology and ore deposits
of the thesis area is largely of a reconnaissance nature
although
adjacent regions have been the subject of more detailed studies,
The most detailed and accurate maps of the area ar. the Sparta
and Halfway 15-minute quadrangles.
Additional maps include the Pine
sheet, a U. S. Geological Survey 30.mfnute quadrangle published in
1915, and various planimotric maps prepared by the U. S. Forest Service.
Complete aerial photographic coverage was made in 195k and photographs
are available through the U. S. Department of Agriculture, Comuodlty
StabilIzatIon Service.
The earliest known geological investigations In and near the
thesis area were those of Undgren (22, pp. 561776).
Undgren's work
was concerned primarily with the various mining districts and their
gold production.
His report Includes a reconnaissance map, and a
brief description of rocks and ore deposits of the Eagle Creek mining
district.
Smith (42, pp. 94-95) described a partial section of the
Martin Bridge limestone exposed near the Paddy Creek confluence,
1is
interests were concerned with the occurrence end correlation of coral
reefs in the
riassic of North Merica.
Swartley (44, pp. 1-229)
reported on the ore deposits of eastern Oregon and described some of
the more important mining operations in and near the thesis area.
LIvingston (23, pp. 6947O8) discussed some of the principal faults of
northeastern Oregon and their relation to topographic expression.
Ross
(38, pp. 1-74) made a reconnaissance survey of about 460 square miles
In the southern pert of the Wallcwa Mountains and his report includes
a reconnaissance map and description of the principal rock types In
the thesis area.
Gilluty (5, pp.
-6k; 6, pp. 181; 7, pp. 336-352;
8, 1*119; 10, pp. 1)94) made several detailed geologic studies rn and
near the thesis area,
More recent work In the Wallowas and surround-
Ing area includes that 0f Smith and AlIen (1+3. pp. 1-61+, and various
unpublished masters and doctorate theses.
GEOGRAPHY
PP*ys I ography
The thesis area Is In the foothills of the southern Wallowa
Mountains, a topographic unit which Ross (38, p. 10) called the
plateau region, as distinguished from the adjacent rugged mountains
to the north and the seml.arid plains a'ong Powder River and afluvlum"
filled PIne and Eagle Valleys to the south.
The positIon of the
mapped area in relation to physiographic features of the region Is
shown in Figure 1.
The area, when viewed at a distance from the southwest, appears
as a moderately sloping basaltic plateau of low irregular relief,
Closer Inspection o
the plateau shows that It consists of several
sloping surfaces which become progressively more Irregular and broken
at lower elevations.
Altitudes range from about 3200 feet along
Eagle Creek to approximately 7400 feet near Suvait Point In the north
east corner of the area.
Topographical development is either late
youth or early maturity.
Drainage
The principal drainage wIthin the thesis area
s Eagle Creek, a
perennial strean flowIng to the southeast and joining Powder River in
Eagle Valley.
The str.en heads In the Wal Iowa Mountains approximately
9 miles north of the thesis area at an elevation of about 7680 feet.
it* over.a)) gradient is approxImately 141 feet per mile and about
114 feet per mIle in the thesis area.
The discharge of this strewt
240
46
1,90
U
46°
1200
I
121
22°
I
--
0
T,//amook
)
II7OO
454o ________________________________
-;T---c--------------------------------j-L
rtfi.L..
¶
Grande
Enterprise
'"WoHowo
450___
(
Salem
/
Yonno Boy
)
I
)
//
if
\\
\
Corvallis
La Grande
A/sec Boy
'\
\\
urucm\H
North
I
'
ThfY\
/
C.
,
)
.
(
Vale
I
Coos
Rome .
GrI
ford
44 25
Klamath Falls
42°
FIGURE I.
Index mop of Oregon.
27°OO
Lakeview
Inset shows relation of thesis
450
Afl
\
(
C
/
\\
/
/
/
Eugene
ater.
1oseph
)
44°_
AREA OF INSET
/ -------%\Enteprls.
?
area to regional
physiogrophic
features.
_°
has been
easured about 8.1 miles north of its confluence with the
Powder River and results are shown In the following table.
Eagle Creek water discharge and related dataa*
Table I.
tar year
ischprge cf
1910.1911
Nay 16-26
9l9
Maximum: 1,640 cfs 5/10/10
1952-1953
August 16
247
MinImum: 55 cfs
1953-1954
August
128
Drainage area: 170 sq. miles
* (49
,
5
2/6/l+
250; 50, p. 290; 51, p. 290)
Averege of eleven days
Principal streams tributary to Eagle Creek in the thesis area
include East Eagle Creek, a perennIal stream heading at an elevation
of about 8,200 feet in the rugged wilderness area to the north; Paddy
a small perennial stream heading near the Amalgamated mine at
Creeks
an elevation of 6,240 feet In the northeast portion of the thesis are.;
and Little Eagle Creek, also a perennial stream heading about two miles
north of the thesis area at an elevation of about 7300 feet.
Climate
The climate of the thesis area Is subhumid to humid with warm
suamers.
Average annual teneratures range between 45 and 500F. with
suiiner highs and winter lows of 106 and
and seasonal variations are great.
-22°r., respectively.
Daily
PrecIpitation Is moderate and
judged from adjacent areas, It Is probably between 15 and 30 inches
a year.
The average length of the growing season 1
159 days and the
overage dates of the lest and ft rst ki 1 Ung frosts are May 8 and Octo-
bar 14, respectively
The records of the U. S. Weather Bureau at Cornucopia, Halfway,
Mchland, and Sparta, Oregon are gIven In the table below;
Table 2.
Climetological data for stations near the thesis area.
0ff. Ave.
Station
Record
Cornucopia
1928'.'56
Halfway
1936-56
1+7.13
Richiand
1945-56
50.33
Sparta
1891-26
45.20
Ave.
Max. Temot.
°F. Ave.
14th. Tenet.
I nches
Ave. pat.
144.41
*
57.7
-
22.12
-
10.58
32.8
20.97
Vegetat kin
The southern slopes of the Vallowa Mountains are characterized
by a dense to moderately dense stand of coniferous and deciduous
forest species.
On the lower valley slopes end a1og strean courses the princi-
pal vegetation includes Douglas-fir Peudotsuga ienzies11), Engelmann
spruce (Picca ene1mørtnI), black cottonwood (Poouhi
aspen (Poouij
tri.chocara),
Jojd), and various species of willow (Salix sp.).
On higher elopes ad ridges ponderosa ptre (Pinus on4ercj) Is the
dominant conifer and Is usually found in mixed stands with Douglas-fir,
grand fir (JkbIes grnd1s) and a deciduous understory of serviceberry
(1anchIer sp.), aider (Alru.
other shrubs.
p.), wild cherry (i!runus sp.) and
With the exception of the conifers, all these species
hay. forag. value, and with the associated grasses and weeds, are
goad for grazing.
For a mare corlate description of th. vegetation occurring In
the thesis area, the Interested reader Is referred to the recent work
of Head (15, pp. l.2i49) Who gives a detailed discussion of the plant
tazonomy and ecology for the East Eagle Creek drainage.
GEOLOGY
Strati grhy
The rocks exposed within the boundaries of the thesIs area range
in age from Permian to Middle Miocene and consist of altered lavas,
graywacke, limestone, shale, slltstone, basalt, and tonailte.
A fw
deposIts of Recent terrace gravels and alluvium occur along princIpal
drainages.
Table 3.
GeneralIzed section of rock formations In the thesis area
ThIckness
Irstem
Series or Stage
Recent
rmatln
In feet
Alluvium
Terrace gravels
gen < 20
170 - 400
Miocene
Middle Miocone
Columbia River
basalt
1000
Triassic
Uppermost Karnic
and Rhastic
Hurwal formation
3500
Triasslc
Upper KarnIc
Martin BrIdge
2000
4000
2000
3000
1500
format ion
Triassic
Middle Karnic
lower Sedimentary
series
Triassic
Albite granite
Permian
Clover Creek
greonstone
4000 1
11
CLOVER CREEK GREEN STONE
The Clover Creek greenstone was named by Gtliuly (6, p. 6) from
exposures along Clover Creek In the northeast corner of the Baker
quadrangle where the section consists of altered volcanic flows and
pyroclastics with subordinate conglomerate, limestone, and chart.
SimIlar rocks in or near the Wailowa Mountains have been described and
mapped by Ross (38,
p. 21) and by Smith and Allen (43, p. 7),
DistributIon and Topographic Expression
The largest exposures of greenstone occur In the southwestern
and north
central portions of the thesis area.
Better
and more acces
sible exposures of these rocks, however, occur along {olcomb and Little
Eagle Creeks near their confluence with Eagle Creek a few miles south
of the thesis area. In these latter localitIes, erosion by stream
action has removed the overlying Columbia River basalt, exposing a
fairly large section of altered volcanic rocks, which (38, p. 21) un
doubtedly represent the eastward extension of similar rocks described
by GIlluly (8, p. 21) In the Baker quadrangle.
Surface expression of the greenstone is essentially that of low
syssnetrically rounded hills, rarely more than 300 to 400 feet In relief.
Protruding outcrops are typically developed an the ridge crests and on
the sides of gullies and streams. The best of these latter exposures
occur along Eagle Creek about 2 miles south of the Paddy Creek con
fluence.
Here, the greenstones on both sides of the stream form fairly
resistant, Jagged outcrops 50 to 250 feet in relief.
Some kn1felike
ridges descend the slopes and produce local changes in the course of
12
the stream.
'-. .'- ,d
__,,_1r
Figure 2. Greenstone outcrop near the head of
Ledge Creek southwest corner of thesis area.
Lithology and Structural Features
Greenstones of the thesl
area Include altered extrusive lavas
and associated graywacke and minor laterbedded pods or lenses of massive and congiomeratic limestone.
A typical hand specimen of the altered lava Is grayish-green or
purplish-green with visible
pnenocrysts of plagioclase set In a fine-
granular to dense groundmass.
Shear structure, often
a distinct schistosity, Is conon.
In the west
characterized by
central portion of the
thesis area, near Dark Canyon, the lavas are exceptionally dense and
nonporphyritic, and contain
bornite, chalcocite, and native copper.
Qraywacke occurs in close association with the altered lavas.
It was distinguished in the field by the presence of visible quartz.
The largest occurrence of these rocks lies between £rrtre Gulch and
Deepsey Creek in the southwest corner of the thesis area.
Massive and conglomeratic limestone lenses and pods are interbedded in the greenstone.
They occur as narrow or Irregularly shaped
bodies ranging In width from 20 to 1000 feet and about 50 to 5000 feet
In length.
Most of the outcrops have slight relIef, sharp frregular
surfaces, and a distinct northwesterly trend.
conglomeratic limestone occurring in sec. 13
A large exposure of
T. 7 5.
R. 43 E. Is
characterized by a poorly sorted mixture of pebbles and cobbles of
greenish chert, limestone, basalt, and greenstona.
The greenstones of the thesis area have undergone a complex hls
tory of metaorphlsm and consequently are difficult to classify as to
original composition.
RelIct textures and minerals suggest that the
original rocks were mostly andestes and volcanic graywacke.
This
Inference Is in partial agreement with Ross (38, p. 25) who described
the greenstones In the north central part of the thesis area as ande
site, and also with Swartley (L4, p. 122) who described similar rocks
on Goose Creek as trachytic and andesitic.
Volcanic graywacke has not
been previously recognized as a member of the Clover Creek greenstone
in the thesis area or in the surrounding region where the units of thIs
formation have been described.
The principal occurrence of the gray-
wacke (i.e. between Dempsey Creek and Empire Gulch) lies in the area
shown by Ross (38k Plate 1) to consist of feisite, which he considered
as a fine-gralned marginal phase of the albIte granite (38, p. 1,6).
Results of the present study do not support Ross' theory of the
ii.
existence of a fine-grained marginal phase. Significant evidence con-
tradictory to thIs theory is (I) the presence of an observable contact
between the athite granite and the rocks In
a gradational contact between the two
question1
does not exist;
Indicating that
(2) the presence
of aliogenlc volcanic rock fragments as essentla! constituents of the
rocks in
Indicative of sedimentary rather than intrusive
question1
origin; (3) en overthrust rather than intrusive contact between the
rocks In question and the Martln Bridge
formation1
and (4) the apparent
absence of a marginal phase rock (and occurrence of greenstone) In
other areas where such rocks would normally be expected.
Patrography
PetrograpMc study has shown that the greenstones in the south-
west portion of the thesis area are characterized by the mInera'
assemblage typical of the greens.chist fac1e
and that the greenstones
in the north central portion of the thesis area have a mineral assemblage belonging to the hornblende-hornfe)s fades.
Greenschlst:
Shear structure is the most dJst1rctIvc feature of
the greenstones In the southwest portion of the thesIs area. Under the
microscope the rocks are seen to consist of what may best be described
as
smeared mixture of finely divided iron ores, leuco*ene, and chlor-
Ite, crlss'crossed
by innumerable calcite and chlorite veinlets.
Variable amounts of secondary quartz, aibite, epidote, and green blotite
may also be present.
Bornite, chaicocite, chaicopyrite, and native
copper occur with ca1cite, or independently, In veins and patches.
Whore these latter minerals are abundant, the weathered surfaces of the
A
B
C
Figure 2a. Microscopic illustrations of greenstone textures.
A. chlorite and calcite veins and
patches. B. Epidote- and biotite-filled amygdules. C. Biotite-filled arnygdules.
VI
rocks may be coated with greenish copper carbonate stains. The less
deformed rocks are characterized by numerous feldspar phenocrysts
(about 0.5 to 1.5 ram) set
ma
brownlsh-'black, dense groundeass of
iron ores, leucoxene, chlorite, and lesser amounts of quartz, epidote,
and pyroxene.
The typical mineral assemblage is albiteepidote-
chlorite-calcite (-quartz'actinoUte). Accordingly, the rocks are
placed in the quartz-alblte-muscovite'chlortte subfecies of the green.
schist fades (4, p. 219).
Plagioclase (An..8) in these relatively undefonamd rocks occurs
as stubby or elongated phenocrysts and as fine aggregates with quartz
In the groundmass. Most plagioclase is 41c1ouded with minute Inclw'
sions of dusty Icon oxlde, epidote, and scaly plates of white mlcas,
chlorite, and actinolite. Twinning on both the albite and pericline
laws was observed In many
crystals1
the twinning laamllae being gener*
ally wide, evenly spaced, and usually bent.
Chlorite is particularly abundant, occurring within the feldspars
or as a groundeass alteration and loss coamonly as small Irregular,
radiating clusters. Most chlorite Is pale green, weakly to strongly
pleochroic, slightly birefringent (about .005 or less), and shows
anomalous blue or purple interference colors. Chlorite In the ground
mass probably formed before shearing or contenporeneousiy wIth shear
lng during earlier stages of regional metamorphism whereas the sym*
metrical and radiating clusters of chlorite apparently have formed
subsequently to shearing as their symamtry Is preserved.
Although not abundant, epldote 1.s present In all thin sections
17
and generally occurs as minute individuals, scattered throughout the
groundmass or as granular aggregates surrounded by chlorite.
properties are variable
Optical
moderate to high blrefringence, parallel to
slightly inclined etnction, end colorless to slIghtly yellowIsh-green
pleochroism.
Variations in birefringence indicate a fairly
wide range
of coositIon (52, p. 448).
Prehnite, occurring as radiating fibers in
an
interstitial rela-
tion to chlorite, was found in small quantities in one th3n section.
Fyfe and Turner
p. 170) discuss prehnite as a stable member of the
greenschlst fades and conclude that Its occurrence probably represents
metrph1sm of even lower grade then that indicated by epidote miner-
als.
Relict augite is a typical constituent of the groundmass, occurring In small quantities as minute irregular grains or in euhedral
crystals, many of which display lamellae
twinning and zonal structures.
Alteration to epidote and chlorite Is typical.
Calcite and quartz are commonly distributed In small amounts
throughout the groundniass.
They are also found to
limited extent
assocIated with patches of chlorite and epidote where these minerals
are altering from pyroxene.
Hornblende
fe:
In addition to earlier regional metamorphism
greenstonoccurring in the north central portion of the thesis area
have been thermally metamorphosed and are characterized by the assemblage, plagioclase-hornblendeudlopside (-quartz-brown biotite)
senting the hornblende hornfels fades (k, p. 205).
repre-
18
Most hornfelsed greenstones are bluish'. or gray1shgreen, very
flne"grained, and rarely
show megascopicafly visible phenocrysts.
They are extremely hard rocks and break with sharp, irregular form.
Plagiociase (Anj52) Is generally present In considerable quan
titles, but rarely of sufficient size to facilitate optical determina.
tions.
It is particularly characteristic as minute xenobiastic grains
scattered throughout the groundeass end as relict phonocrysts that
range in length from 0.5 to 1.5 mm.
Aibite periclin. and Carlsbad
twinning are relatively àommon; complex penetration twinning was also
noted.
'Cloud1ng of the plagloclase is widespread but less Intensive
than in greenstones of the greenschlst fades.
Mineralogical and textural features of these plagioclases reflect,
to a certain degree, the various types and intensIties of metamorphism
to which the rocks have been subjected (37, p. 261).
The wIde range
In composition (alblte.i.Iabr.dorite) Indicates that metamorphism has at
no time been of sufficient intensity (or duration) to effect complete
chemical reconstitution of the rocks. Twinning, especially of the
complex type, Is a strong Indication of relict feldspar (35, p. 247);
so also are the subhedral and euhedral phenocrysts (48, p. 506).
bIotIte is another common constituent of the greenstones, occurring as fine, green
and/or brown shreds distributed in large or srnll
amounts throughout the groundmass or as flakes clustered In aggregates.
This mineral Is the recrystallization product of two different perIods
of metamorphism; the green variety reflects regional metamorphism and
the brown variety denotes thermal metamorphism.
Green biotite Is the more common mica, being characterIzed mainly
LJJ
by numerous inclusions of Iron ores and rims of altóration products
leucoxene, chlorIte, and epldote.
Brown biotite is more typically associated with hornblende end
diopside In recrystallized anygdaloidal cavities.
Actinolite is a common constltuent of the groundrnass, occurring
as plates or fibers with weak pale green pIeochroism
This mineral Is
commonly associated wIth chlorite, calcite, and epidote.
Green hornblende, mostly In amygdaloidal cavities, is associated
with brown shreddy biotite, intermediate plagiociase, pyroxeno, and
minor munts of sphene and Iron oxides.
Diopside is typically developed in anygdaloldal cavities and
loss commonly In the groundmass.
Porphyroblasts are rare and where
found generally show Irregular form, Incipient zonIng, and basal
parting; twinning t
seen in tne large crystals, but Is more common of
the microlites occurring 1n the grounthaass.
Most diopsida is colorless,
but a few crystals exhibit weak pleochrotsm.
The
undeass of these the mall y metamorphosed rocks contains
abundant iron oxides, ranging In sIze from minute dustlike particles
to kernels 1
mm
in diameter.
Leucoxene is equally abundant, occurring
In small, Irregular metamorphosed patches and as narrow rims around
ilmenite or titaniferous magnetite.
Generally, a faint outline of
primary trachytic texture Is seen under these opaque
products.
sooty" alteration
Where the affects of metamorphism have been severe, the
groundeass becomes a mat of finely fibrous biotlte and anphlbole with
subordinate pyroxene, epidote and quartz or plegioclase.
Sphene is
found as inclusions in hornblende, plagioclase, end iron ores.
20
Carbonatizatlon is equally well displayed in these rocks by
an
abundence of calcite-filled veins and vesiles, and the repIaceet
of aMbole and pyroxene by calcite.
ConversIon of flmiite and
titaniferou
agnetite to leucoxene
was noted,
stud
yduj: A particularly Interes-'
- metainorjhosed
ting occurrence of thermal ly etam3rphosed amygduies was noted In
greenstones occurring on the ridgu northwest of the Amelganated Mine.
The best exanples were found in s.alcs G-172 and G177, collected along
the ridge In the SW cor., Sec. 35 1. 6
S0,
IL 41 E.
The sgniflcance of vesicular or amygdaloldal minerals as indices
of metaorphism probably was first noted by ilarker (14, pp. 292296),
who described their occurrence in the associated igneous and metanorphic rocks of the Shap granite, We.stmareland.
In his account of the metaiorphosed
by the
o)
anygdules of the Skye basalts, re-
corded an Interesting conversion of Ii
feldspmrs, acconan led
Later, larker (12 p.
-soa zeolites to lime-'soda
formation of epidote, hornbiende, and
blotlte at the expense of chlorite. M4Llatock (28, pp. 1-33) In his
excellent discussion of the zeolites and associeted
Tertiary lavas around
Ben More, Mull,
minerols In the
stated that the
metanorphism of
amygduies produced prhn1te, epidote, pyroxeno, hornblende, garnet,
sphene, end aibite.
Laterworkers have recorded similar f1ding. Plchanuth (36,
pp. 157-160) noted the occurrence of plagioclese (An35) in amygdules
of the Ungadballt traps, IC.adar District., Mysore, and concluded that
the feldspar was probably derived from the alteration of some zeolitic
21
minerals which originally filled the vesicles.
I4oehlman (29, pp. 329-
331) found that the amygdules in andesite dikes in the San Juan Moun'
teEns, Colorado, contained albite..ollgoclase in addition to the usual
minerals.
Ho concluded, however, that the arnygdules wr probably of
deuteric or late magmatic origin.
Recent workers (11, pp
332340) have recorded cloudy quartz,
leucoxene, opal, palagonite, and calcite.
Le bas (20, pp. 29l296)
noted that the zeoil$es commonly form the bulk of amygdules and 1n
variably occur In fibrous or radiating masses.
Ha suggested that
feldspars formed from these zeolites during metamorphism would tend
to follow the original texture.
Gliluly (7, p. 228) in his discussion of keratophyres of eastern
Oregon noted that inconspicuous anygdules were cosrzroniy present in the
greenstones.
Such amygdules generally contained euhedral, water-clear,
albite crystals whose centers are filled with quartz and chlorite.
Amygduies In the greenstones nortleest of tne Pmelgarnted Mine
are somewhat similar to those described by OflIuly, but contain a more
diverse assemblage of minerals.
Here, amygdules are of two types:
those that are spheroidal or ellipsoidal In form, ranging from I to
5 mm in length and consisting of either shreddy brown biotite or epidote
with minor amounts of pyroxane
hlbole,
quartz5
plagloclese, and
ores, and those that are Irregular In form, ranging from about 2 to
10 mm In length and consisting almost entirely of granoblastic plaglo-
des. (An23.8) with lesser amounts of arhiboIe, pyroxene, biotit.,
epldote,
atite, sphene, and quartz.
22
Figure 3. Photomicrograph of metamorphosed amygdule. Dark
perimeter due to abundant Iron ores, leucoxene, and fine
shreddy biotite. Inside margin Is mostly clear plagioclase
with minor quartz. Central portion is composed of green
and brown blotlte with less amounts of a,hbo1e.
50X
Ellipsoidal amygdules are invariably surrounded by a narrow
border of shreddy brown btotlte, leucoxene, and ores which grade into
a "sooty's groundmass containing Innumerable plagioclose microiltes
arranged In a fluidal pattern about the amygdules, an arrangsRsnt which
eliminates any question as to the primary origin of the anygdules.
This concentration of iron
ores near the margins of the vesicle
is apparently a comon characterlsitc.
For example, M'Llntock (28,
p. 17) noted ... a marked feature In some of the slides Is that the
rock for some distance around the vesicle is very much altered and
shows a large development of chlorite and black oxide of iron
The lnsfde margins of the
mnygdul2s
generally consist of a
narrow linIng of water-clear quartz or piagloclase or
tars of epidote
sometimes cius
radiating into the center of the cavity. ørownlsh-red
shreddy blatlte is generally found in the centers of the cavities and
appears to radiate outwards toward the wails in the fashion suggested
by La Bas for fcldspars derived from radiating zeolitic
masses.
Irregular amygdaloidal structures, as previously noted, consist
almost entirely of
granoblastic sodic plagloclase.
Individual plagio
clase grains are larger in the central portion of the cavities and
become smeller as the walls are approached.
twinning are coenoaly present.
Pericline and albite
The outside borders of these amygduies
are also characterized by a concentration of Iron oxides, but to less
degree than the ellipsoidal blotite-Filied tes.
Veins and associated fractures containing sodic plaglociase are
coiancnly found cutting an
ygduIe or connecting one with another.
Depositlonal Environment
A marine environment of deposition has been fairly well estab
lslhed for at least the greater part of the Clover Creek greenstone
(8, p. 26). Relations In the thesis area are also indicative of marine
deposition as shown by the occurrence of limestone and volcanic gray..
wacke.
24
Age and Stratigraphic Relations
The Clover Creek greenstone occurring in the southwest portion
of the thesis area Is undoubtedly Permian in ag. as greenstone may
be traced with little or no interruption into areas (6, Plate 1; 38,
i4) that have produced Permian fossils or have been definitely cor'
related with such fossU.bear1ng strata,
The greenstones occurring
in the north central portion of the thesis area are tentatively desig*
neted as Permian also.
The base of the Clover Creek greenstone Is not exposed In the
thesis area.
The formation Is ovorlain by the Lower Sedimentary
series and by Tertiary lavas and Quateraary gravels where the younger
preTertiary rocks have been removed by erosion.
The coeplexity of structure and the intense deformation of the
rocks do not permit an accurate determination of thickness.
Gilluly
(9, p. 22) suggests a thickness of at least 4000 feet and possibly
much greater for the formation in the Baker quadrangle.
ALBITE GRANITE
In the Sparta quadrangle, grantic rocks of sodic conosItion
are exposed over an area of nearly 40 square mIles (38, p. 45).
These
rocks were originally described by Undgren (22, p. 585) who referred
to them as 'i... normal soda granites in which orthocisse Is almost
entirely wanting ..."
Gilluly (6, pp. 6341) in his classical study
of these rocks referred to them as albite granites.
Ross (38, p. 45)
also termed these rocks as albite granites, but applied the definitiOn
in a general rather then a restricted sense.
The term albite granite is retained In this thesis for purposes
of correlation, both to the reader in aiding Identity with previous
writings and to the literature itself which en'ploys the term, as a Sort
of standard for rocks of this particular coiosItion, It is pointed
out, therefore, that the albite granites of the thesis are not such
in the strictest sense (i.e. conplete absence of potash feldspar), but
are tonal ites and sodaclase tonal i tcs.
Distribution
and Topographic Exptession
The entire southwest corner of the thesis area, with the excep
tion of a small 'area of basalt, consists of a dIstinct, hypidlcmorphic
granular sodaclase tonalite and tonalit..
Good exposures of the albite granite in the thesis area are few
as almost .11 of these rocks are deeply weathered and yield satles
Which crumble when struck with a hawaer. The best exposures of the
albite granite occur In the stream valley of GooCreek approximately
800 yards west of the thesis boundary and can be convanlently reached
by a newly constructed logging road. In this locality the stream has
cut a fairly deep trench through the rai tic rocks exposing about a
300
to 1O0"foot section.
The typical outcrop here is fairly resistant
and forms Irregular exposures of variable relief, generally not greater
then 25 to 75 feet. The surface of these rocks as observed from a dIs
tance is usually dark grayish or brown, but at closer range is much
lighter in color. The lIghter tones of green1shbrown or buff seen on
close examination result from surface oxidation and a filmy accumula
tion of weathering products, mostly limonite, clay minerals, and
26
chlorite.
Figure 1
Albito granite outcrop on east side
of Goose Creek approximately I mile
south of Daddy Lode Mine.
Lithology and Structural Features
Freshly fractured albite granite is light gray, usually of a
decided greenish shade, with small clusters or single crystals of
nearly white feldspar.
The rock is firm and tough rather than hard
and brittle and breaks with an irregular granular surface.
Porphyritic
and granular textures are usually conspicuous and close exauinatlon of
a fresh surface shcws numerous phonocrysts of stubby, clear quartz and
of milky white plagioclase, many of which have striated cleavage faces.
Phenocrysts of
phibole are connonIy present, but are not conspicuous,
and small black specks of magnetite may also be detected.
27
A striking light-colored variation of the albite granite was noted
on the east slope of Goose Creek in the thesis area0 Characteristic
features are local, Irregularly scattered
occurrence1 low relief1
almost complete lack of any dark constituents1 end nearly white or
slightly yellowish porcellaneous eppea.raice. Giliuly (6, p. 67) noted
similar rocks (presumably In the sane general locality, I.e. Goose
Creak) and accredited their
. chalky ... but firm epp.arance ..,"
to intense shearing.
Decomposition is so prevalent a feature of the aibite granite
that It may be considered as one of the rock's chief characteristics.
The depth of weathering varies with the topogrephic position, generally
from I or 2 feet In stream valleys to as much as 50 feet In upland
positions. Fresh s1.s are found only along stream courses, recent
road excavations, and In old mine workings.
Pet rography
The albite granite In the thesis area, wlth few exceptions, is so
highly decomposed that fresh sa,les suitable for microscopic study
were collected from adjacent areas. Consequently, most of the samples
studied were taken from the outcrops exposed along Goose Creek less
that a mile west of the thesis area.
albite granite is a t1cal
Texture: Textural variation of th
characteristic. flypidlomorphlc"granular (grenitic), porphyritic,
mlcrographlc, and cataclastic textures,
Including
gradational and com-
binational variations have been observed.
The principal texture, however, Is grani tic with usually uniform
grains averaging between I to 4 me.
Embayment of plagloclase by quartz
was noted in many thin sections and was regarded by GIlluly (6, p. 73)
as evidence of replacement.
Sutured and interlocking contacts are
typical.
Porphyritic textures are characterized by phenocryste of plaglo.
Glu, and quartz, with plegiaclase being the most abundant.
Most
phenocrysts of plagioclase are euhedra) to subh.dral, and 0.5 to 5 me
long.
Quartz is often rounded and embayed and generally larger than
plagioclase.
The greunónass, averaging about 01 me in grain size,
Is a fine, equigranular aggregate of quartz and clear plagloclas..
Micrographic texture occurs In several distinct forms.
The most
meon Is a uniformly radiating pattern of intergrown quartz and albite
which may be 2 to 3 me in diameter.
A small variation of the t1roset
tes" Is also typical of the groundeass.
These are about 0.2 to 0.5 me
In diameter, occur independently or as clusters Sn gradational contact
with each other, and are usually surrounded by a very fine sugary margin
of quartz and clear albite.
"SraIrpceralt' texture, an Intergrcwth of
albit. and quartz, was noted In one thin section.
Cataclastic texture varies from an aggregate of angular frageents
which still retain the nature of the parent material to extremely fine
mylon$tes which cameonly show faint lineation.
jsj: Plagioclase, mostly ranging in coeposition from
sodlc lbite to intermediate oligoclase, constitutes the most abundant
mIneral of the albite granite.
Most plagloclas. Is subhedral with
lath*lIke fore and blunt or jagged terminations.
in finer*textured
rocks it occurs as anhedral grains or slivers lntergrown with quartz of
similar form.
sharp.
Albite and pericline twInning are common and usually
In crushed and brecclated rocks, however
twinning Is less
distInct or lacking and when present Is fnvarlabiy bent, undulatory,
and masked by extensive alteration products.
feature of the plagioclase.
Zoning is also a common
The zones are of the normal oscillatory
type, uniform, and seldom exceed
or 5 to a crystal.
Embayment of
plagioclasa by fingerHke extensions of quartz was noted In several
thin sections.
These embayments are distinguished from the normal
marginal shallow indentatIons
which are also common, by their
ent preferred alignment parallel to the cax1s of the feldspar.
par
ThIs
alignment is befleved to have resulted from replacement along twinning
leflae.
AlteratIon of plagloclasc Is confined largely to the more calcic
cores of zoned crystals, to narrow strips along cleavage planes, and
to crystals that have been crushed and brecciated.
Zona) alteration
Is usual ly the most common and the entire central zone can be con
lete'
ly altered to a fine scaly aggregate of sericite, apidote, and calcite.
These smme alteration products plus shreds of brown blotite are also
typically developed along the cleavage planes of many piagloclase
crystals that lack zonal structures.
Rocks that have been subjected
to crushing and breeclation usually contain plagioclase frageents that
are coe,letely masked by a mixture of fine shreds and plates of serl"
cite and variable
Quartz Is
unts of associated alteration products.
parently present In two generations.
Early quartz
occurs as anhedral grains Interlocked with adjacent minerals In granular rocks.
t.ater quartz occurs as poikilitic patches 3 to 5 mm In
dianeter having plagioclase inclusions, as an interstitial component,
and as Isolated stringers and hook-shaped blabs In plagioclase.
Strain shadows, undulatory extinction, and a distinct biaxial
character are typical features In earlier formed quartz, but are con
spicuously absent In later quartz.
This relation suggests that prior
to albitization and silicificatlon the granitic rocks were subjected
to considerable compressional stresses,
Amphibole is present in small anounts in rocks characterized by
granular and closely allied textures and conspicuously absent in rocks
having cataclastic textures.
Tt
varieties of ahIbole, common
hornblende and hastingslte, occur and are invariably in close association wIth each other,
Common hornblende, apparently of earlier origin, is present In
lesser quantities than hestlrigslte. and the estimated ratio of these
two minerals Is about 1:9.
hornbiende Is strongly pleochrolc in
:raddishbrown; it shows birefringence about 0.O2C
angles ranging from 26 to 33 degrees.
common and twinning rare.
.002, and extinction
Typical auphibole cleavage is
A few subhedrai crystals were observed,
but most hornblende is extensively resorbed and altered to chlorite,
ore, and epidoto.
}iastlngslte occurs In anounts up to abut 10 percent of the rock,
It Is moderately p%eochroic In light bluish-green, optIcally negative,
and has extinctIons varying from 16 to 19 degrees.
Crystals are
Invariably enhedral and commonly poikIlItically enclose zoned feldspar
phenocrysts.
The gradational relationship of common hornblende and hast1ng'
site has been discussed by GI Iluly (6, p. 69, 7i) who accredited the
dev. Iopment of hastings I te at the expense of common ho ml ende to
"... post manatIc attack ..." by permeating soda-rich solutions.
The gradation.) relationship of those two minerals Is well displayed In
thin sections of rocks from the thesis area.
A typical transition will
show a gradational variation In pleochroism and birefringence, end a
decrease In extinction from common hornblenda to hastingsite.
Altera-
tion products such as chlorite and Iron ores may mask a large portion
of these gradational crystals, but optical continuity is so close that
It precludes the possibility that such crystals may represent two
unrelated minerals.
(flotite Is apparently present in two generations.
Early brownish-
red blótlte occurs In small emounts only In granular rocks.
It Is
always anhadrel, may or may not show blrdseye extinction, and commonly
contains zircon Inclusions.
Alteration to chlorite, iron ore, and
leucoxena is common.
Biotite, seemingly of later generation, Is typically the shreddy
brown variety and Is found both in granular and In cataclastic rocks.
Usually It occtIes narrow veins which cut feldspar phenocrysts, but
It has also been noted as lnthvidual shreds In plaglociase and as a
principal grounchnass constituent.
Epidote is a common minor constituent that occurs In both granular
and cataclastic
ent
It
IS
rocks1
and may represent the principal maf Ic constitu
partIcuIary coaon as a plagloclase
alteration product.
occurring as granular aggregates with chlorite and sericite along
cleavage planes and in zoaal cores.
grounthnass
Epidote
has also been noted as a
constituent.
Iron ores in decreasing order of abundance Include mógnetite,
pyrite, Iine;tlte, and hydrous iron oxides.
Magnetite, cacunonly present in small wiounts occurs as skeletal
crystals and as small Irregular blebs interstitial to
feldspar.
Meg-
netlte also Is a typical alteration product of amphibole and biotite.
Pyrite was found only in rocks having cataclastic texture.
It
Es usually found as minute (about 0.5 nun) podshed grains (a few
idiomorphlc cubes noted) with a marked tendency to develop along or
adjacent to fracture planes and zones of extensive brecciatlon,
iImattite although identified In only one thin section, Is probably present In at least trace amounts as a separate mineral and as
an lntergrowth with magnetite.
lydrous iron oxide, probably mostly limonite, occurs principally
as a surface oxidation product
of weathering. Under the microscope it
was noted as narrow zonal aureoles surrounding pyrite and magnetite.
Sphene, apatlte, and zircon, In decreasing order of abundance, are
presint In small but persistent quantities.
Sphene was noted In over half
of the thin
sections studied,
It
is chiefly secondary, associated with chlorite, but a few narrow wedge
sh,ed grains of fairly regular outline within brown biotite may be
regional and siliciflcatlon, and albitization crystallIzation,
normal during granite albite the In minerals of Development
s Paragenesi
0.05%.
100.0
100.0
100.0
3.2
4.3
1.8
I
1
I
1
I
1
-
-
0.1
0.1
0.2
I
I
1
I
I
6.3
I
0.3
I
T
42.0
47.3
354
56.4
.W
enounts In present minerals
I *
100.0
I
0.2
I
0,1
-
5.2
10.2
I
36.2
51.5
.&12
I
0.3
3.6
3.0
42.3
51.5
fl.t
iematlte
Sphene
Epldote
Calcite
ChlorIte
roducls 0 on 4Jteçati
Zircon
Apatitc
Ilmenite
Magnetite
Minerals cessorv
A,hibole
1otite
Quartz
Plagioclase
Minerals Principal
cent. per volume In granite aibite of Modes
4. Table
common. Is plagioclase in lamellee twinning parted and fractures along
calcite of Penetration
piagiocisse. and quartz of clasts enclosing
partially Interstitial, is it rocks cataciastic In
rocks. granular in
piaglociae of product alteration an as amounts sparing
In and texture
cetaclastic with rocks in only abundance in occurs Calcite
observed. also were rutile of twins kneoshaped
few A
blotite. primary and feldspar in Inclusion
conon
a Is Zircon
crystals. anhedral to subhedral minute as biotite and plagioclase,
with association in principally occurs at1te
h1bole,
primary.
metamorpMsm was determIned by teturai and mineralogical relationships.
orma! £EY5311iZat10fl
The coarse texture of the albite granite
indicates that solidification was a relatively slow process with nor
ma) crystallization accompanying the failing temperature, although
there Is evidence of corrosion
resorption, and replacement due to
mineralizers and deuterlc solutions, such as the corrosion of magne
tite, feldspar, and quartz, and the zonary replacement of oligoclase
by more sodic plagioclase.
Apparently the earliest
minerals to crystallize from the magma
were the euhedral minor accessories; apatite, zircon, end rutile as
indicated by their presence as inclusions In ores, feldspar, and
ferromagnasian minerals,
Some rutlie iwey be of metamorphic origin.
Nearly contemporaneous magnetite and ilmenite (and probably
titaniferous magnetite) were next to crystallize.
A small amount of
ilmenite and somewhat more of the magnetite occur as idlomorphic
crystals showing more or less solutlonal alteration.
Magnetite IS also
present as a by-product of reaction, being one of the principal pro-
ducts In the breakdown of amphibole and botite.
Conunon hornblendc and piagioclase are nearly contenporaneous as
both these minerals show interstitial and sub-ophitic relationships
with each other. Nornblende was noted as containIng grains and 1dbmorphic crystals of magnetite.
The first plagioclase to crystallize
was andeslne, and the relatively large size of the crystals attests to
the great length of time Involved In their growth.
idith continued
crystallization, the residual magma became more sodic, as shown by
zone) structure and slight but progressive change in the extinction
angle of albita twinning lella toward the borders of the crystals.
Brown blotite Is tentatively placed as postanphIboIe in accor
dance with Bowen's (2, p. 61) discontInuous reaction series, as no
dependable textural or mineralogical relationshIps between these two
minerals was observed,
Blotite was, haver, noted as being partially
embayed by plegioclase, indicating earlier or at least contemporaneous
crystallization with that mineral.
Subbedral mdgel1
crystals of
sphene have been noted as polkilItic Inclusions in biotite, suggesting
Its early crystallization with respect to its host.
Primary quartz was one of the last of the princlpal constituents
to crystallize as Is indicated by Its occurrence, In granular rocks,
as an interstitial component in relation to plagloclase.
Aib[t,!.j*t[gn
iUlcjficatlpn:
Albitization and silIcifIcatlon
constitute the most widespread deuerlc alteration in the late stage
crystallization sequence.
The changes that took place according to
GIlluly (6, p. 65)
"... are attributed to later maatIc and postmaat1c
replacement of the almost completely solidified quartz
diorite by solutions derived probably through filter
pressing from lower portions of the sane mass.
These
solutions were guided, at least In part and probably
entirely, by brecciated zones In the quartz dlorite.0
The corrosive action of the residual solutions is clearly dis*
played in many of the thin sections studIed.
Almost all minerals, with
the except1on of early accessory
constituents1,
show solutlonal effects
and crystal llzatlon of quartz In corrosion channels.
eldspar
are
litvarlably characterized by rounded corners and marginal embayment,
and not uncomeonly are completely engulfed by quartz.
Biotte and
hornblende are also embayed and contain recrystallIzed çuartz blebs,
CrystallIzation of albite as marginal growths on more calcic plagloelase and as vein and fracture fillings Is widespread.
e&ioje1 m4!phism
Host of the specimens of elbite granite
thi area display at least incipient metamorphism.
The
typical metamorphic assemblage is quartz-.lbte-sericlte'-chlorlteepidote ('-brown blotite), which corresponds to the quartz-elbite-
epidote-'blotite subfacies of the greenschlst fades (it, p. 223).
Chlorite Is the most abundant and widespread member of the
assemblage, but does not generally formmore then 0.5 to 3 percent of
the rock, usually the lesser.
Itoccurses fen-shed masses inter'
stitlal to quartz and plagloclase,snd as an alteration product of the
forrornagneslan mInerals.
Epidote, sphene, and Iron ores are ttcaI
associates.
Serldte Is particularly abundant as a plagioclase alteration
product in rocks that have been severely sheared and brecciated.
it Is
enerally found as minute flakes 0.05 to 0.! an w1de showing fairly
high
Interference colors.
Elsewhere, sericite has been noted in unde'
formed rocks Interlaced with chlorite, epidote, and blotite.
occurrence it is typically developed as
tween
0.01 and 0.05 me long.
In this
minute shreds and flakes bc
Brown shreddy biotito Is a connon but not abundant member of the
assemblage.
it Is typically developed as a groundmass coiistituent in
cataclastic rocks and as a vein constituent In plagioclese and quartz.
Age and Stratigraphic Relations
The sibite granite was originally assigned to the post-Triassic
by Llndgren (22) Plate 64), although he did not observe the relations
between the granite and Triassic sediments (aZ, p. 734).
Ufluly (6,
Pite 1) assigned a Late Cretaceous (?) age to the alblte granite and
advanced the hypothesis that the rock was originally emplaced as a
single mass of quartz dlorlte which was later partially altered by
sodic solutions (5, p. 17; 6, pp. 65-81),
In a later report Gilluly
(8$ p. 89) noted that none of the IntrusIve masses of the Baker quadrangle were emplaced durIng Lower or Middle Triassic time and also
mentioned that the albite granite near Eagle Creek tad been found J*
truding known Triassic rocks.
The intrusive relatioisnlp between the athite granIte and In-
assc rocks referred to by Gilluly was originally noted by Ross in
1921 durIng his reconnaissance survey of the southern Wallowas.
stated In his report (38, p. 47) that
Ross
a1b1te granite is intrusive
Into the Clover Creek greenstone and Its finer-greined marginal phase
cuts the Martin Bridge forniation.
This jntru1ve relationship has not
been recognized in the thesis area for reasons previously discussed
(page 14, under Clover Creek &reenstor.e),
The age of the albite granite is here considered to he post
Clover Creek and pre-Upper Triassic
an tl-
basis of direct and Indirect
evidence observed from the rocks and their relationshIps in and near
the thesis area.
hear the western boundary of the thesis area (road cut, NE cor.,
SC. 35, 1. 7 S., R. £43 E.) the alb$te granite shows direct evidence
of intrusive relationship to the Clover Creek gre.nstone by containing
completely Isolated, xenolIthlc masses of the latter.
Indirect evl
dance suggesting a pre-Upper Triassic age includes the finding of
grani tic pebbles In the Lower Sedimentary series which show mlner&
logical and textural features nearly identical to those of the aibite
granIte.
The albite granite has also been regionally metirnrphased as
Indicated by the presence of minerals belonging to the greenschist
faciesj Early Cretaceous granitic rocks in northeastern Oregon do not
show evidence of regional metnorphIsm.
LOWER SEDIPIENTMY SERIES
A particularly convnon phase in the sedimentation history of many
geosyncilnes Is the accumulation of great thicknesses of a distinct
llthologic suite, the general characterizing features of which are:
varied assemblages
f unstable minerals, high matrix content, dark color,
predominance of clestics, scarcity of fossils, and the presence of
rhytivaic and/or graded bedding.
Most of these features are displayed by the Lower Sedimentary
series which is a thick, orogenicphase sequence of sediments in the
northern part of the thesis area.
Th. term "Carbonl ferous (1) Sedimentary Rockst was adopted by
Ross (38, p. 26) for U... the predominantly sedimentary strata
39
stratigraphically below the Martin Dridge formation (Upper TriassIc)..'
in his description of these rocks in the Eagle Creek drainage area,
Ross states that they
are for the most part sandstone, conglomer'
at., and cherty slate with a few
strata of probable
Igneous origin."
Smith and Allen (43, p. 8) in a later report termed the sane
strata as a Lowr Sedimentary series and described them as consisting
essentially of
shales, sandstones and minor ianses of Umestone."
Results of the present study are for the most part In accordance
with the findIngs of these earlier workers, although no interbedded
igneous rocks were found,
Distribution and Topographic Expression
11* Lrnwer Sedimentary series crops out In a roughly concentric
belt around greeàstonee in the north central portion of the thesis
area which have been tentatively correlated with the Clover Creek
greenstone on the basis of relict textures and mineralogy. A small
exposure of the sediments also occurs along Eagle Creek where they
consist of conglomerate.
West of the thesis area, near the mouth of
Osrit Canyon, conglomerate and graywacke were noted,
Surface expression of the Lower Sedimentary series Is variable,
the
unt of relief and degree of slop, being strongly influenced by
three factors: 1) type of .k, 2) attItude of the beds, and 3) degree
of metemorphism.
As a general rule, the conglomerates form the most lresslva
outcrops, many of which stand 50 to 60 feet high.
Fairly steep slopes
and jagged or knobby outlines are characteristic.
Occasionally, great
and degrees) (30-50 moderate is sandstone the of attitude
structurat
the where areas In absent generally are outcrops Protruding
surface. slope the of trend general the to angles right at strike
and vertical almost or vertical are them composing beds the
the to form
their
owe example,
northwest- the descending
the of attitude structural
for Creek, Lagle
ridges razorback few
East
A
that fact
of slope facing
beds. underlying
tne upon dependent coainonly
are graywacke
of composed areas In slope of degree and relief of amount The
Creek. Gold to stream
tributary small along conglomerate series
Sedimentary Lower of outcrop Typical 5. Figure
area. the of portion central north the
in Creek Gold of streams tributary along developed
are features Such
well particularly
sandstone. surroundIng resistant less the above ces
prominen- resistant as stand conglomerate of masses ship-like isolated
parallels that of the slope surface.
Here, the typical surface ex
presslon Is I to 2 feet thick, chippy talus coaposed of hard, buff*
colored
angular frageents
irregular outcrops of low relief may also
be present, their existence being largely determined by the presence
of local bedding distortions.
Lithology nd Structural
esturss
The Lower Sedimentary series In the thesis area consists, In
decreasing qumntlty, of red and green graywecke, massive to moderate
ly bedded pebbly conglomerate, dark gray limestone, and a few lenses
of chart.
Graywacke, as defined by PettiJohn (34, p. 301), ts the principal
rock type and makes up perhaps 60 to 70 percent of outcrops In the
mapped area.
Nost of it shows excellent graded bedding, Jointing, and
In same recently cut streme canyons, the grawacke is .graylsh'.green or
reddish, hard, tough, and frequently cut by quartz velniets and less
coamionly by calcite valniets.
On upland slopes It weathers locally
to a dirty greenish or reddlsh'.brown rock of varying hardness and
resistance.
Two particularly characteristic features of these graywackes are
their predominantly reddish color and monotonous presence of rhythelt.
cally graded beds.
The reddish color Is due to an Ironrich clay.y
matrix which generally constitutes nearly 50 percent of the rock, and
also to the presence of abundant red shale and claystone particles.
Graded bedding was found In practically every graywacke outcrop
and was continuously eaployed as an aid In determining the structural
k2
attitude of the strata.
A typical graded bed In these rocks averages
about 70 to 80 iun in width and exhibits a textural gradation from
coarse at the base to fine at the top.
The coarser portion usually
forms about twoN.thirds of the bed and is somewhat lighter in color.
Each bed rests on the surface of the next lower bed with the contact
between the two generally being sharply defined by the
difference In
other hand, a series of graded beds may
have their entire flne-gralned portions stripped away so that dlstinc.
grain size and color.
On the
tion between each layer Is not immediately apparent and the outcrop
has the appearance of a massive, coarse-gralned
sandstone.
Figure 6. Typical exanpie of graded bedding In
Lower Sedimentary series graywecke.
$ltm
structures and other related soft-rock deformattonal
features are characterIstic of the graded beds.
microfaults are particularly convnon.
Clearly defined
These structures generally
occur in closely parallel sets, cut across several graded beds
dip
about 60 to 70 degrees, and show sip displacements ranging from a
few millImeters to 15 to 20 cm.
Not uncommonly a set of microfaults
are sharply terminated at an erosional surface between two graded
beds that lack their fine-gralned portions.
Under such conditions
the faults provide a means of determinIng the top
strata.
nd bottom of the
Load casts depressed Into a fine-gralned portion of a graded
bed by a thick accumulation of coarser material In an overlying bed
are also con*non.
Such structures range In size from small well-like
depressIons 2 to 3 cm in depth to minute surface cranulatlons resemb)Ing symmetrical ripple marks.
Their use as top and bottom criteria
was eeployed continuously.
Coarse to medium polmdctic conglomerate constitutes the second
most abundant flthologlc unit of the Lower Sedimentary series In the
thesis area,
In detail, these rocks generally occur as Irregular and
discontinuous lenses, intercalated in the graywacke, but extensive
outcrops occur in some localities (I.e. upper Paddy and Gold Creeks)
suggesting thicknesses measurable in hundreds of feet.
The conglomeratic beds are not confined to any particular horizon
In the formation, as they were noted to be In contact with the greenstone In the north central portion of the thesis area and also to lie
within 200 to 300 feet of the overlying Martin arIdge formation on
Paddy Creek.
Jhen fresh, the conglomerates are reddish.. or greenish-gray,
highly siliciftéd, end extremely hard; when weathered, they are
commonly Ught brownish-gray or buff) less well Indurated, and of
variable hardness and resistance.
The constituent granules, pebbles
and cobbles are angular to well rounded, poorly sorted, and have corn-
positions which Include graywacke, red siliceous shale and claystone,
fIne-grained basic to intermediate volcanics, red and green chert,
quartzite, and granitic rocks.
Small, discontinuous lenses of fine-
to medium-grained graywack., lnterbedded In the conglomerates, are
fairly common.
Such lenses were also found having a graded se4uence
and thereby provided essential top and bottom criteria.
The principal structural features of the conglomerates Include
locally confined vertical and diagonal Jointing, assocIated fracturing,
and less commonly, small normal faults which show 2- to 3"inch d1s
p1 acement.
The limestones are typically dark gray or black when fresh, and
weather to various shades of lIght gray or buff.
They are usually
massive and generally form conspicuous outcrops.
Principal exposures
occur near the head of Gold Creek and at the head of Twin Bridge Creek.
The bedded cherts are generally light gray when fresh and weather
to a yel lawish-brown.
Some of the best exposures of these rocks are
found on 4per Little Eagle Creek where they are interbedded with the
graywacke.
Patrogrhy
The principal textural and coosit1onal features of the
graywackes are: predominant red and green color, poor to fair sorting,
low roundness and sphericity, coarse to fine grain sizes, predominance
of rock fransnts and low grade metamorphic minerals, scarcIty of fo
sits, low quartz content, md an abundant, partially recrystafllzed,
I ronr1ch mstrlx.
Texture:
A typIcal microscopic field of a graywacke thin section
consists of a varied assemblage of poorly sorted clestic grains that
range in size from the lower slit limit up to about I millImeter.
Grain boundaries are seldom distinct, and appear to merge with the
matrix, which Is typically a dirty reddishbrown paste conosed of
Ilmenite, hematIte, leucoxene, chlorite, sericite, and variable amounts
of clay, probably an lron.irlch montmorl iloni to or nontroni to.
The bulk
of the matrix is coiosed of particles of silt size and Is coeeionly
present in sufficient quantities to prevent Interlocking of large
detrital grains.
In addition to the I4slltu matrix, the graywackes
contain minor amounts of authigenic carbonate (ankerlte 7) and silIca,
but rarely In excess of 20 percent of the rock.
The average roundness for several hundred grsi ris of the graywacke
was estimated (18, p. 81) and found to be approxImately 0.26, corres
ponding to the lower limit of the subrounded class (34, p. 59).
This
coaparatively low value suggests that the predopositional history of
the sediments was of moderate duration and that conditions of trans'
portation and accumulation were sufficiently uniform over a wIde area.
Coiimosltlpn:
Significant coaposltlon features of the graywackes
are: I) the percentages of mineral and rock constituents are fairly
consistent between semples wIdely distributed
over the thesis
2) the feldspar is chiefly plagloclase In th
range olIgociase'ande-
area,
sIne, potash feldspar being rare or absent, 3) rock fragments,
especially fIne'gralned sediments and basic to intermediate volcanics,
are abundant and generally constitute 40 to 50 percent of the detrital
fraction, and 4)
detrltal quartz seldom constitutes more than 8 per
cent of the rock and is generally
more angular and of larger size
than
associated grains of different composition,
Feldspar, primarily sodic pagioc1ase, comprises on the ave.rc
18 to 2.2 percent of the detrital grains of the graywackes.
Much of
the feldspar has undergone considerablepostdepositionai alteration
Involving the development of whitemicas, serlcits, fine scaly epidote, and other products which gIve the feldspar a dirty or turbid
eppearance. Other postdepositlorial alteration is reflected by matrix
replacement along detrital grain margins and to less extent by albite
end carbonate replacement.
Quartz is a coanon constituent of the graywacke, but is rarely
abundant.
it Is generally quite angular In form, occurring as narrow
slivers or more typically as triangular fragments with sharp concholdal and embayed margins. Most quartz is somewhat coarser and more
consistent In grain size than other mineral constituents. Postdepositlonal alteration is confined primarily to solutlonal etching
and replacement by carbonates.
Lithic constituents of the graywacke generally form about 45
percent of the detrlta) fraction and about 23 percent of the entire
47
rock
CanosIt1ons are extremely variable, Including reddish siltstone
and mudstone, f1negralned basic volcanics, siliceous Umestone, and
minor anountsof granitic rocks.
Grain sizes range from silt-sized
mudstone and siltstone particles of the matrix to granitic cobbles
2 to
Inches In dlemeter.
Table 5.
Modes of Lc*ier Sedimentary Series Graywecke
Mintpl constituent
J.21
Feldspar
lZb
J.
r of S
I9
18
20
22
19
20
20
Quartz
7
5
7
8
5
6
Matrix
42
56
39
40
32
42
Lithic fraents
27
16
25
20
28
23
Carbonate
x
x
x
9
12
4
Chlorite) epidote, biotlte,
zi rcon, pyroxene ?, pyri te
6
3
7
4
3
5
100
100
100
100
100
100
Fossils are rare in the greywacke and when found are Invariably
frapentary pieces of larger shells. identification is ivoss1b1e
clue to recrystallization and other alteration effects.
The grnitic material occurring In the conglomerates I s charac'
terlzed by a f.lnt pinkish tint, medkn granular texture, and
a
tonalite conositIon with abundant stubby clear quartz, sodic plaglo
ciase, and chioritized ferromagnesian minerals as th. principal con-
stituents. Under the microscope the principal texture is bypidiomorphic granular.
A crude form of micrographic texture is also typical.
being characterized by
nn- and hooked-shaped blebs of i.Iuartz
enclosed by plagloclase. Principal minerals are quartz, plaglociase
(An915), ferromagneslans, and iron ore. Apatite and zircon are
accessory. *iteratlon products include sphene, epidote, chlorite,
ilmonite, calcite, and kaolin. The ferromegneslan minerals are not
easily distinguished due to extensive alteration. Pseudomorphs of
chlorite after
blotite and interleaved shreds of chlorite and biotite
were noted. The former presence of ahiboie Is suggested by the
aggregate of chiorl te-calci te-sphene.
MetamorpM se
Most of the Lower Sedimentary series in the thesls area shows at
least a low grade of regional metamorphism typical of the greenschlst
fades, as is evident by recrystallization of the matrices of the graywacke and slight shearing which causes Indistinct boundaries between
grains. In addition, quartz franents commonly show a small 211 and
undulatory extinction, end the twinning )amei lee of piegloclase are
commonly bent and undulatory.
Locally, in zones of xtreme shearing and brecclation, more
advanced stages of metamorphism are evident. Near the head of SullIvan
Creek, for exle, highly schistos. and recrystallized equivalents of
the graywacke are found.
Provenance
Conos$tionaI features of the Lower Sedimentary series show that
coeiex condltlons prevailed In the source area, Such conditions
Include;
I.
The lithology of the source area consted of lavas,
fine'gra1ned sediments
and granitic material in decrease
lug order of exposure or availabIlity.
2.
Sporadic and local crustal disturbances caused minor
displacements, warping and shearing of the strata.
3.
Topography of adjacent land areas was probably la
the l.t. youthful or early mature stage of development,
characterized by high relief.
1+,
A relatively uniform cool teaerate climate with
seasonal precipitation apparently prevailing.
Vegetation
was probably not abundant.
The abundance of ndesltic end basaltic rock particles composing
the graywacke and interbedded conglomerate strongly suggests that the
principal parent material contributing to the great thickness of the
Lr Sedimentary series was an extrusive volcanIc series of basic to
Intermediate composition.
Fine.gralned sediments, either overlain, or
sore probably intercalated with the volcanic series, were less abun
dent.
High, or at least moderate, relief for the source area is sur
mized on the basis of the apparent maturity of the L.ower Sedimentary
series and on the general knowledge that such rocks (graywacke) are
derived from the rapid erosion of tectonic belts (18, p. 132).
MATURITY INDICES
Average graywcke (3kb p. 509)
Lower Sedimentary
greacke
Qtz/f. iispa
Qtzchert/fe1.dsaar'rocJcs
2.7
1.2
3.0
1.3
The highly angular nature of the graywacke constituents and the
content of unstabl, residue (I.e. feldspar and rock frageents)
high
Indicates Incoaplete weathering and rapid removal of the parent
material.
Dispersal
Transfer of the various lithic and mineral constituents of the
graywacke by turbidity currents Is supported by the presence of car.
tam
characteristic structural features typical of turbidity current
sedimsntation,
each graded
bed,
These are
) graded bedflng,
(a)
poor sorting in
(3) lower contacts of each graded bed usual ly sharp,
(4) presence of load casts
and other soft rock deformat.ional strucw
tures, (5) interbedded slide conglomerate, (6) irregular shale Inclu-
slons, end (7) occasIonal frants of shallow marine fossIls.
The
absence of such features as wave ripple marks, channel scour, and
croisbedding Is further evidence of deposition In deep water.
Deposltional Environment
The depositlonal environment of
the
believed to have been a subsIdIng marine
Lower Sedimentary series is
trough
or basIn separated
from the source area by a continental slope favorable to the accumuls
tion of detrital material and the development of turbidity currents.
51
Forces responsible for triggering the turbidity currents could have
orIginated In the subsiding depasitional environment, on the continentel slope, or Within the source area.
Whatever the origin of trigger'
Ing, It. seems probable that It was uniformly intermittent as indicated
by the persistence of only slightly variable structural, textural, and
caa,osItjonal features of the rocks.
The Interbedded conglomerates of the Lower Sedimentary series are
Indices of crustal disturbances of greater magnitude than those coin-
cident with deposition of the graywacke.
The presence of limestone
and bedded chert, on the other hand, indicates that relatively quiescent conditions also prevailed.
Age end Stratlgraphlc
elatIons
There is no direct evidence as to the age of the Lower Sedimentary
series in the thesis area.
In the northern Wallawas Smith end Allen
(43, p. 9) collected fossils from the formation which Indicated an
Upper Triassic (middle Karnic) age.
Stratigraphic relationships between the Low.r Sedimentary series
and C lover C reek greenstone are uncertain in the thesis area due to
metinorphic obliteration of reference planes In the greenstone.
in-
spection of the geologic map, however, suggests the possibility of an
unconformity.
Along Paddy Creek the Lower Sedimentary series appears to be
conformable with the overlying Martin Bridge formation as indicated by
closely parallel structural attitudes on both sides of the contact.
The thickness of the Lower Sedimentary series cannot be deter'
mined with accuracy due to the conlIcated folding that the rocks have
undergone.
A conservative estimate of thickness based on graphic
analysis of the formation between Gold and Packsaddle Creek Is between
2000 wd 3000 feet.
Ross (38, p. 29) suggested that the thickness of
the formation near Sullivan Creek (a smell portion of which occurs In
sec. 34e, 1 6 S., R 444 E.) may be somewhat greater than 2000 feet.
MARTIN BRIDGE FORMATION
The Martin Bridge formation, ned for Martin Bridge (38, p. 32)
which formerly crossed Eagle Creek near the Paddy Creek confluence, is
a calcareous formatIon containing masve exposures of bluish-gray
limestone, associated black and grayish calcareous shales, and minor
lenses of highly indurated hey sandstone.
Distribution and Topographic Expression
Several excellent exposures of the Martin Bridge formation occur
ln the thesis area,
The largest and most irapressive exposure Is almost
continuous along th. eastern slope of Eagle Creek conencing from a
point Just south of Basin Creek and extending northward for an undetermined distance beyond the thesis area.
The more prominent outcrops
are coaposed of extremely hard end Irregularly weathered limestone
which generally form vertical to steeply Inclined cliffs end ridges
that rise some 50 to 150 feet above the less resistant associated
53
shales.
Erosional and solutlonal caverns, most of which are 5 to 15
feet wide, are often found along the basal portion of the outcrops,
their origin resulting largely from the erosional action of Eagle
Creek.
FIgure 7. Massive Martin Bridge limestone outcrop on
east side of Eagle Creek approximately l/ mile
north of Paddy Creek confluence.
Paddy and East Eagle Creeks aio afford interesting stratigraphlc
arid lithologic sections through the formation, but accessibility wd
observation are somewhat restricted
to steep slopes arid a dense
forest cover.
Lithology and Structural Features
Approximately 55 to 60 percent of the Martin Bridge formation
consists of extremely hard, bluish-gray, massive or locally bedded or
brecciated limestone.
The remaining
ko to 15 prcent of the formation
Is composed of fine. to coerse1y-Iinated shalas which contain a rich
Invertebrate fossil fauna and a Umy sandstone which Is apparently
restricted to the eposed base of the formation.
Most limestone is massive, weathers to a light blulsh..gray color,
and Is rough to the touch, Hand lens Inspection shows the rock to
have a grainy appearance.
On fresh surfaces the limestone Is usually dark gray or black,
has concholdally fractured surfaces end emIts a strong odor of H2S.
Remnants of pyrite, usually In part altered to hematite or limonite,
are coa*non but not abundant.
In a few localities, however, fairly
euhedral pyrite crystals wer, found in quantity, their dimensions
varying from less than I
em
to about 10'12 nvn.
In localities where
pyrite Is abundant the limestone Invariably displays a fair to medium
degree of stratifIcation, jet black color, and an abundance of Inverto
brate fossIls. Although fossils
have been recovered from
the limestone,
they are usually In too poor a condition for accurate identIficatIon.
Chert, occurring as minute grains o1 microscopic dimensions
to large nodules 3 to 5 Inches In dianter, Is a particularly coevaon
constituent of the limestone. The chert varies In color from ye1lowish
green to black.
Lenses of this materIal are not common; they are
more than 2 to 3 feet long and average I to 5 inches wide.
seldom
All large
chert nodules and Ienes were found in the more massive limestone and
are apparently absent or scarce in the stratified limestone.
Jointing of the limestone Is one of Its most characteristic
55
features, especially in the more massive outcrops0
Generally in a
single exposure three prominent and fairly consistent sets may be
observed, two at right angles to each other end the third cutting the
first two at any angle.
Another outcrop, perheps 200 to 250 yards
eway, will show an equally consistent set of joints, but of conleteIy
different attitudes.
Variation in structural attitudes, however, Is not confined
solely to jolntlng; minor folds, faults, and bedding planes may show
marked change in plunge, dip, or strike wIthin 5 to 10 feet In adja
cent or continuous exposures.
Generally the ca1creous shales of the MartIn Bridge formation
show less deformation than the 1jmestone.
This condition is attri-
buted to a finely lm$nated structure and the ability of one bed to
slide over another In a manner resembling the way one might fold a
pack of playing cards.
Where folding has been more intense, however,
the shales are Invariably sheared and are characterized by easily
erodable outcrops coosed of closely packed pencil-like surfaces.
Interbedded 5- to 10-inch limestone layers irs these localities are
characterized by typical boudin structure where the more brittle
limestone has parted along tension fractures and the snore ductile
enclosing sheles have yielded more or less plastically under shearing
stresses.
There are very few localities within the Martin Erid
where fossil shells cannot be found.
shalcs
Diligent search, except in the
more sheared areas, will invariably yield at least rensriants of Flalobia,
IL
//
:.
I
*' -
I
s_lb
:'.
! ,:
i
A
,
F.;
;.
..'
.
(;,rc:i.
p
k
t .i
57
Juvavites, and related species. A typical
shale bedding plane is
usually conietely covered by overlapping Impressions and casts of
the shells, The use of these sheil-'impressed end casteci surfaces as
an aid in determining top and bottom of the strata was unsatisfactory
as the underside of a shale plate would show an equal number of convex
and concave casts or Impressions as the upperside.
At the base of the Martin bridge formation a section of highly
indurated, massive, hey sandstone was noted. ThIs unit Is particu"
larly well exposed on Paddy Creek where it occurs in conformable
contact with underlying fine-grained red and green sandstones of the
Lower Sedimentary serbs. The unIt is approximately 16 feet in width,
light grayish In color, end extensively jointed.
Petrography
Principal textural and compositional features of the Martin
Bridge limestone are: bluish'gray color, fineness of grain, crystal
lographic fabric, presence of clay, low magneslan content, and the
presence of reefebuliding corals and crinold stems.
ur: A typical limes one thin section wIll generally show a
finee to medlumecrystafline texture with Individual crystals averaging
between 0.05 and 0.25
nun in dianeter. Crystallographic orientation
usually predominates over dimensional fabrics, but all variations
bee
tween the two were observed, Many thin sections are characterized by
a faint rusty shade; this condlt.lon Is accredited to the hydration of
pyrite in rocks that have been subjected to shearing. Not uncoiinuon)y,
a thin section wifl show a horsetailelike network of hairlike veins
that contain ilmonite end an iroa.rich clay.
Crystal boundaries are
seldom distinct due to recrystalized clay particles, llmonIte, end
dark carbonaceous residues.
M1neraLoicai comeostion:
The Martin Bridge limestone consists
essentially of calcium carbonate and effervesces freely in cold dilute
hydrochloric acid.
Microscopically, the limestones are characterized
by a scarcity of accessory constituents.
A conservative estimate of
dilute acid insoluble material ranges between 0.2 end 0.8 percent of
an original 30.gram sle and averages around O.A percent for 10
specimens studied.
The most ccmeon accessory constituents In order of decreasing
abundance are: chert, plagloclas., quartz, epidote, pyrite, and magnetite.
Potash feldspar, garnet, and zircon were noted in one specimen.
Dolomite end enkerite arc probably present as indicated by chemical
analysIs, but they were not
dentIf led under the microscope.
Chert constitutes about 75 percent of the insoluble residue in
the limestone.
In thin section It is typically found as minute gran
ules distributed along calcite crystal boundaries or as larger (0.2 to
0.3 em) irregular blabs or rosette-like patches within the calcite.
Most, If not all, of the chert is authigenic in origin and micro-
scopic evidence suggests that some may be postdeposltionah
Many acid
insoluble chert particles show an indented chevron-like pattern on
surfaces that were formerly in contact with rhombohedral cleavages of
calcite crystals.
if the chart were detrital, such chevron patterns
would not be expected.
The Irregularity of particle form and the
53
sharpness of the chevron patterns preclude the possibility of transportatlon.
IeIdspar generally cont1tutes about 10 to 20 percent of the
Insoluble constituents, but It has been noted In quantities up to
about 45 percent.
Almost .11 feldspar Is plagloclase ranging in
composition between intermediate elbite and sodic oligoclase.
Crys
tel form is poor and angular fragments averaging 0.2 to 0.5 mm In
length are most common.
Clouding, due to alteration and crsrystalli
zatlon products, is distinctly less advanced as compared to the
calcite.
Potash feldspar was noted in one thin section.
uartz Is generally present in trace amounts up to about 5 per
cent of the Insoluble constituents.
It is angular or subrounded and
seldom found In grains larger than 0.5 mm in diameter.
Strain snadows
are common and birefringence may range up to low first order yellow.
Epidote Is present In trace amounts only, but was noted in *
most all thin sectIons and in all insoluble residues studied.
It
occurs typically as minute individual granules, either Interstitial
or within calcite crystals.
Pyrite constitutes the principal ore of the Ilmestones and can
usually be found as anhedrel or euhedral cyrstals Irregularly dIstrI
buSed on any smed surface.
The most common occurrence of this mineral,
however, is In and near shear fractures.
Chart nodules In the lime-
stone also contain pyrite.
ChemIjJ comoositloji:
The chemical composition of limestones,
as indicated by Pettijohn (34, p. 383), reflects rather closely their
mineralogical composition.
Probably the
signifIcant feature noted
during the siile chemIcal analyses was the unusually large emount of
hydrogen sulfide generated when a pulverized sale was Innersed in a
dilute hydrochloric acid solution,
Also significant was the reiative
ty large anount of black carbonaceous residue remaining after comple"
tion of the reactIon.
made of this
Although no weight percent measurements were
,
it is estimated to average between 0.1 and 0.2
percent.
A complete chemical analysis of a limestone sle collected
along the road about 2.8 miles above the Eagle"Paddy Creek confluence
is as follows;
Table 6.
AnalysIs of limestone smiie collected along the road about
2.8 miles above Martin brIdge, sec. 8, 1 7 5, ft 44 E.
.1. G. Fairchild, analyst (30, p. 134).
Si02
A1203
Fe203
FoQ
MgU
CeO
10.92
3.21
0.25
0.65
45.36
0.22
0.45
0.90
K0
H2u
1102
0.21
36.24
0.07
trace
0.03
o.ik
P205
$02
Mnd
Fe2
Organic matter
04,4k
100.67
Specific gracity
2.l
Dopes1 tional Environment
That the l4artln Bridge formation is unquestIonably marine Is
shown by Its faunal and lithologic association.
The problem of Its
categorical definition (I.e. platform, basin, or geosynclinal),
however
Is less easily determined,
The platform environment of limestone deposition Is eliminated
firstly by the fact that the area end formation In question Is s!tu
ated within a region of known tectonIc instability and secondly by
the fact that the Martin Bridge formation dOes not display the neces
sary depositional characteristics of tectonic neutrality, such as
minor thicknesses (10's to 100's of feet) which extend without marked
change in character over very broad areas (ki, p. 110).
The only sure method of distinguishing between the basin and
geosynclinal depositional environment would be to determIne the th1ck
ness of the formation and to construct an Isopach mep.
This procedure
of course, Is out of the question due to the limited area of investige
tion and colex$ty of structure therein.
Prob*bly the best argument in support of the geosynclinal rather
than the basin environment of deposition Is the coincidence of known,
or Inferred, geosynclinal conditions In northeastern Oregon existing
prior to and during the Late Triassic.
Lithologies signify that depo.
sitlon was often altered by increase or decrease In subsidence, the
former being Indicated by the dense, black, and cherty limostones of
the formation, and the latter by lighter colored and more foulllferous
types.
A basin deposit.ional environment, on the other hand, might
62
become closed to an open seiay during periods of slow subsidence and
due to saturation of the enclosed waters precipitate beds of evapor*
(tic c*lclu
accumulation.
tion.
carbonate and other salts typical to this type of
Also, such salts era not found In the Tr1ssIc fonw'
It has been shown that the evaporation of sea water in a
closed basin cannot give rise to thick carbonate deposits - see water
1000 meters deep would give on'y a few centfrneter
of limestone (25,
p. l55l56), hardly enough to account for the thick Umestone sections
observed In the thesis area.
On the basis of regional relationship
d observod lithologias
w1thin the mapped area, the Martin Bridge foritatfon is, therefore,
designated as a marginal geosyncllnal deposit which accumulated In an
area Where deposition was essentlafly equal to, and sometimes lagged
behind, the rate of subsidence.
Climatic conditions prevailing during Martin Bridge time is best
indicated by the reef-building corals contained In the limestones.
Smith (1.2, p. 92) points out that modern reef-building organisms are
found only In the tropIcs, and it Is only reasonable to assume that
they heve always been confIned to regions where the water had a tropical teap.rature.
Age and Stratigraphic Relations
The Martin Bridge formation has long been noted for Its fossil
content.
tJndgren (22, p. 581) made several collections which were
Identified by Dr. T. W. Stanton as including specimens of Halobla,
atmnonite fragments, PentactIni5 columns, and a cast of a gigantic
gastropod which had the form of a very large Iurriteiij or Pe,doIctia.
In 1921, Clyde P. Ross made several collections from the forma
tion which were also referred to Dr. Stanton for Identification,
sp., ia1obia sp.,C1ionIte sp.and
Species included
tr1nts of amnonites, all of which confirmed the Martin Bridge for*
matlon as Upper Triassic In age.
Fossils collected by the wrIter from the formation have been
exeelned by Dr. SimonW. Muller at Stanford University.
A lot col
lected from a sheb outcrop at the east end of Eagle Creek Brldge,
SE
SE*, Sec. 6, T. 7 5., R. uk E. Included HalobLa Si,)
A collection
from this seee locality was also made by R. Q. Lewis, Geologist, of
the U. S. GeologIcal Survey In 1958.2
The collection was referred to
N. J. Silbering for identification and was reported to consist of
4yvavi
and Halobla species.
An age of Upper Triassic, probably
MIddle Karnian or above, was gIven.
The Martin Bridge formation
pears to conformably overlie the
red and green graywacko øf the Lower Sedimentary series.
This rela-
tionship Is particularly well exposed In a road cut along Paddy Creek
at an elevatIon of
prox1metely 4160 feet.
A similar reLationship may
Simon W. Muller, Professor, Stanford UnIversity.
2
June 8, 1959.
Richard Q. Lewis, Geologist, U, 5. Geological Survey.
Nov. 5, 1958.
be found on the northwest facing slope 0f East Eagle Creek at an elevation of about 4640 feet.
Elsewhere In the area the lower contact
relationships are obscured by a thick accumulation of talus.
and unconsolidated terrace and stre
the formation.
Basalt
gravels unconformably overlie
A conservative estImate of thickness for the formation
in the thesis area Is between 2000 and 4000 feet.
NURWAIS FORMATION
The sedimentary rocks occurring in the extreme northwest corner
of the thesis area are referred to the Kurwal formation end on the
basis of fossil and stratigraphic relations are believed to represent
the uppermost portion of that formation.
Distribution and Topographic Expression
The best exposure of the Hurwal formation occurs on the eastfacing slope of Eagle
Creeks
coimnoncing at a poInt opposite the mouth
of East Eagle Creek and continuing for an undetermined distance to
the northwest beyond the thesis area.
Exposures of these rocks also
occur In the vicinity of Lily White Guard Station and near the head of
Dark Canyon.
On Eagle Creek the sedIrnnts are exposed on steeply inclined
slopes that rise over 1000 feet from stream to ridge top.
The surface
of the $ lopes i s characterized by clean and smoothly weathered rock
that reveal excellent detail of internal texture and structure.
Rock
streams, which are easily set In motion when crossed, are typically
developed In narrow (25 to 30 foot) troughs descending the slopes and
also along the sides of razor back spur"rldges that protrude from
the
siopes at nearly right angles.
In other localities the sediments are less well exposed. At
Lily White they form low, smoothly rounded hills nd ridges with welt
developed soils and a thick vegetative covering. Near
the
head of
Dark Canyon erosion has been more severe and fair outcrops occur along
the sides of the canyon and side gulches.
Lithology and Structural Features
The lithology of the Hurwal formation includes black caicareous
argillite and minor amounts of massive limestone
rd congiomeratic
limestone.
Black calcareous argillite Is the principal rock type of the
Hurwel formation.
The unit varies in Its content of calcium carbonate
and In places grades Into silty limestone, but the bulk of the unit is
composed of calcareous and carbonaceous silts in well-lndurated beds
that range In thickness from I/k to 18 inches. Narrow (5 to 10 inches)
lnterb.dded layers of light gray limestone and yellowish sandy shale
are common.
The entire unit weathers to a rather uniform rusty'grey
color.
Massive lenses of limestone are common, and
because of their
greater resistance to weathering are commonly found in the form of
spur ridges. Most of the ilmestones are bluish-gray, but nearly pure
llght*gray and black pyrl tic varieties are common.
Conglomeratic beds
and lenses, gradational to the massive limestone, are extensive In a
few places but not common.
The materials composing the conglomerates
consist almost entirely of allogenlc chert arid limestone with minor
enounts of greenstone and other basic Igneous rock particles.
One of the most distinctive Features of the 1urwal formation
Is
its uniformity of bedding attitude. On Eagle Creek the formation has
a consistent strike, recorded over a two-mile distance, of N 50-60° W
and dips that range between
40_700 SW.
srther to the west, In Dark
Canyon and Sanger Gulch, there is less consistency in
*ttitude, but
the principal trends are similar,
Graded bedding, although not a coiion feature, is well-developed
in a few localitIes. the structure is generally characterized by
a
sequence of distinct and uniform beds, 2 to 6 inches wide, each of
which shows a less well defined decrease In grain size from bottom
to top. The gradation In grain size Is more conspicuous on weathered
surfaces,
Petrogrhy
The principal textural and compositional features of the argit-
lite are dark color, fineness of grain size, high induration and
co
paction, and high sIlica, pyrits, and calcIum carbonate content.
iexture: A typical thin section of the Hurwal argl lii e his a
dense, dark mass of angular to subangular
lt-slz particles enclosed
In a matri, of iron-rich clay and carbonaceous material. ilost thin
sections show an isotropic fabric where all particles
pear to havi
a random orientatIon, but a few showed faint HneatIon or anisotropic
fabric, by an alignment of silt particles. This latter fabric is
believed to be largely postdeposltlonai in origin, resulting primarily
67
from compactIon,
cementation, and slight recrystallization of clay
particles.
nposIt1qn:
Calcium carbonate probably represents between 5
and 15 percent of the average
urwai argililte, although a few may
contaIn 50 percent or more, and would be more correctly referred to
as silty limestones. The rock Is only slightly decoiosed by acid
and then only If the sample has been crushed to pass a 35 mesh screen.
The insoluble resIdue obtained by this method ranges between 85 and
95 percent of an original 30-gram sa1e.
to 75 percent
quartz
10 to 15
Principal minerals are 65
percent calcite.
Accessories
Include
pyrite, chlorite, limonite, white micas, end carbonaceous materials,
X-ray dIffraction analysts of a typical arglllIte sale Indicated the
predominance of quartz and albite.
Pyrite, although conspicuous In
the hand specimen and thin section, was indicated as a minor constitu-
ent, probably less than 5 percent. Grains are between .05 and .005
me
in diameter; most are angular to subangular, with poor spherlclty.
Deposi tional Environment
The conformable relationship between the Hurwal and Martin Bridge
formations (43, p. 14) and their local
similarities In lithology sug-
gest that the depositional environment of the two was essentially
alike, that Is, a marginal geosyncline.
The Increased content of
silt
In the Hurwai formation Indicates
a greater Influx of that material and may reflect, as do the conglomer
ate beds. associated with the limestone reefs, slight uplift and/or
aggressIve wctherIng in the source area.
more
Other diagnostic sedimentary
features Include (1) high organic and sulfids content indicating a
reducing environment and the absence of free cIrculation, (2) limestone
reefs which favor relatively warm shallow waters, and (3) the reported
p. 13) occurrence of welldeveioped ripple marks whch are
characteristic of th. littoral environment.
These features suggest
that the general over'aIi depositlonal environment was somewhat restricted to the open sees, that deposition fk.tuated between the
littoral and epinaritic zones, and that a tropical or subtropic,)
clImate prevaIled.
Age and StratigrhIc Relations
The age of the Hurwal formation In the northern Wallow. Mountains
has been recorded by Smith end Allen (13, p. 14) as uppermOst Karnic
and Noric
Their dating is based on "a good fossil collection within
50 vertIcal feet of the basal contact with limestone of uppermost
Kernic age."
A fossil collection made by the writer (ridge crest, SW cor.,
NE
SW *, NE
, sec. 1, T. 7 5., R. 43 E) and submitted to Simon V.
Muller for Identification Indicates that the Hurwal formation is also
of uppermost Triassic or Rhaetic age.
The diagnostic fos1l suggesting
this age Is Identified by I4uIler1 as a large pelecypod
cf, £.
Conchon sp.
fr*lipsIcus Stqpani. A similar pelecypod submitted to the
Simon V Muller, Professor, Stanford UnIversity.
Aug. 28, 1959.
U.
. Geological survey was dated by N. J. Si ibering1 as Noric or
hhaetic.
Figure 9. Cnchodn sp.cf. £. infrallasicus Stopoanl.
One of the better preserved specimens shown in
original position of burial. A shallow (2 to 3 inches)
horizon has developed on the limestone bedrock.
Length of knife is four inches.
The contact relationship of the iurwal formation with the underlying Martin bridge formation In the thesis area was not
to the complexity of folding and the
absence of good
cal areas. Smith and Allen (43, p. 14) have noted
tion In the
northern Wallowas.
The Hurwal
determined due
exposures In criti-
a conformable rela-
formation Is unconformably
overlaln by Columbia River basalt and Quaternary gravels.
A conserva-
tive estimate of thickness is about 3,500 feet as Indicated by the
section exposed in the northeast corner of the thesis area.
N. J. Silberling, Geologist. P & S Branch, U. S. Geological Survey,
Menlo Park, California.
Sept. 23, 1959.
Side
Figure
O.
view
Conchodon sp. cf. C. infraliasicus Stoppani.
Front view
Approximately O.5X actual size.
a
71
COLUMBIA RIVER BASALTS
The Columbia River basalts, as originally defined by Russell
p. 2023), Included the great mass of dominantly basaltic lava
In the region drained by the Columbia RIver and are undoubtedly named
after the impressive columnar exposures occurring in that region (26
p. 303).
Distribution and Surface Expression
Columbia River levis are widely distributed throughout the
southern Wal Iowa Mountains and conti tute one of the most extensive
formations therein (38, p. 52).
Basalt occurs in the thesis area in
both small and large Irregular patches covering less than one to over
ten square miles,
The total aggregate of these exposures amounts to
about 25 square miles, or roughly 1/2 of the mapped arca
Along the northern boundary of the thesis area the basalts
occupy a topographic position above
500 feet, rising steadily to
elevations above 7000 feet farther north end northoastwedIn the adja*
cent Eagle Cap and Halfway quadrangles.
Southward through the thesis
area the basaits are exposed at successively lower elevations and are
currently being eroded at elevations below 3500 feet In the stream
channels of Eagle, Little Eagle, and Holcomb Creeks.
Llthology and Structural Features
When fresh, the basalts are typically a tough, heavy, dark
brownlsh*gray or black rock containing visible phenocrysts of caicic
piagioclase and cllnopyroxene set in a fine granular groundmass of the
72
same minerals plus small amounts of magnetite, olivine, glass and nongranular deuterlc and secondary minerals.
Near Sumit Peak In the northeast corner of the mapped area, the
basalts are exposed in vertical to steeply Incflned cliffs several
hundred feet high.
thick, are
Generally three to eight flows, each 25 to 75 feet
clearly visible, especially when viewed from
a distance.
naked, brick-red soil horIzons and step-like erosional benches or in-
dentations aid In distinguishing individual flows.
Columnar jointing,
developed locally iii a few outcrops, occurs as closely spaced polygonal
columns
to 15 inches wide and 10 to 20 feet high.
l
Figure 11.
ColumbIa River basalt exposed near
Summit PInt.
73
Figure 12. SpheroIdal weathering of Columbia River
basalt. Photo taken In road cut in Blue Canyon.
Scarcity of vegetation is
an obvious feature in areas underlain
by basalt and Is due largely to the Inability of these rocks to develop
a sofl horizon; heavy spring runoffs, summer thunder showers, end winds
keep the basalts swept clean of weathered material.
A limited amount
of vegetation, principally pines and brush species, Is found, however,
along intermittent drainages, on flat.topped hills, and along moist
zones of baked soil horizons.
Pet rograp hy
Principal textural and compositional
features of the Columbia
River basalt are: fine to medium granular and porphyritic textures,
fluldal arrangement of
acicular and lathshaped feldspar, and the pre-
dominance of calcic plagioclase and clinopyroxene.
Texturet
The principal texture is
intergranular, in that most
interstices between plegloclase laths are occupied by randornly arranged
granules of augite, magnetite, and ollvine. Intersertal texture is
also connon and appears to grade from the intergranuiar type by an In-
crease of interstitial glass, chlorite, c*Iorophae1te, and zeolites.
Subophitic texture, or parUal enclosure of plagtociase by augite, and
semltrachytic texture resulting from subparallel arrangement of feld
spar microlites were also noted.
ongs1tion: Mineraloglcaily the basalts are oilvIne-bearing,
with the anount of ollvine ranging from a trace to about 1 percent.
Calcic plagioclase, cflnopyroxene, and magnetite are principal consti
tuents with olivine, apatite, and glass as typical accessories,
Table 7. Nodes of typical Columbia River basa)ts In volume per cent.
Sv
Conent
l
G26
Plagloclase
Auglte
ilagnetlte
28
32
4
6
Olivine
I
Chlorite
4
5
Chlorophacite
6
2
100
100
Piagioclase (An505) constitutes about 50 to 60 percent of the
rock and occurs as relatively large (3 to 5
), anhedrel to subbedral,
randomly orIented phenocrysts and as minute (.c5 to .5
)
Interstitial
granules and laths.
Albita and combined aibita"Carlsbad twinning are common with the
twinning Iameilae being broad, evenly spaced, and usually sharp.
Alignment of chlorite shreds, white micas, and iron ore along these
twinning planes is typical.
Progressive and oscillatory zoning Is
particularly common among the larger phenocrysts with the central core
having a £ to 8 percent more calcic composition than the margins.
Alteration of plagiaclase Is confined largely to the more calcic
cores which may be completely altered to shreddy aggregates of white
elcas and calcite.
Zonal Inclusions of Iron ore and augite, and the
occurrence of augte between twinning )amellae Is also common.
Clinopyroxene, represented by diopsidic augite and by small
amounts of pIgeonite (7) occurs In two generations.
The earlier one
forms partially resorbed idlomorphic phenocrysts showing typical
pyroxene cleavage, zonal structure, twinning, and extensive fracturing.
iater pyroxene occurs in the groundmass as irregular grains and as
larger (3 to 5 ma) xenomorphlc crystals partially enclosing feldspar
phenocrysts.
These later augite phenocrysts differ from the earlier
pyroxenes by the absence of twinning and zonal structure.
They are
generally colorless, show typical pyroxene cleavage and estimated 2V
ranging from 45 to 55 degrees.
The occurrence of augite as an interstitlal component with res
pact to feldspar Indicates that It is later in the crystallizatlon
sequence or possibly contemporaneous sdth the feldspar.
Alteration of pyroxene Is limited to marginal deuteric develop"
merit of iron ores and formation of chlorite and calcite along parted
cleavages and fractures.
Magnetite constitutes about 5 percent of the typical basalt,
It
occurs as skeletal crystals and as anhedral patches in the groundmass.
Much magn.tlte Is present as secondary alteration products of olivine
arid augite.
The larger skeletal crystals, however1 are primary pro"'
ducts of crystallization which have been elt.red by later deuteric
reacttons with residual liquids.
011vIne Is a common accessory coeonent present In auounts up
to 1 percent.
It occurs as minute anhedral grains less than a mliii"
meter in diemeter and is Invariably surrounded and eayed by magne"
tit. and serpentine.
iddingaite Is present In trace anounts up to about 1 percent.
It
occurs as narrow felted stringers and veins In ollvine.
Glass is a common constituent of the basalts occurring as an
Interstitial caoponent and averaging between I and 3 percent of the
rock.
Most glass has undergon. variable degrees of devitrificatlon
with the development of chloropheeite and chlorite.
These products
plus an Indeterminate ferritic dust renders the groundeass a yellowish"'
brown, semi 'opaque oppearance.
Chlorophaelte occurs as a brownish, partlafly Isotropic substance
In the groundeass and is believed to have been formed by reaction of
later mageatic fluids with ferromagnesian minerals (32, p. i78).
Apatite, a minor constituent present only in small amounts, Is
generally found in association with Iron ores and particularly occurs
along and within skeletal crystals of magnetite.
Most apatite Is
euhedral, occurring as short, stubby hexagonal crystals and as narrow
needles or prisms.
Conditions of Deposition
The problem of origin and deposition of the great mass of
basaltic lav. covering over 100,000 square mfles of the region enclosed
by the Columbia River Plateau was probably first recognized by L.eCente
(21, p. 179).
To him it seemed 'lncredib1e" that such an enormouS
volume of lava could have Issued from the numerous volcanic cones and
mountains situated along the crest of the Hig$ Cascades.
Consequent
ly, LeConte proposed that extrusion of the lava took place under relatively quiescent conditions by fissure eruptions activated by the
same forces which elevated the mountain range.
His theory was sup
ported by carefully analyzed field evidence arid by comparison with
similar orogenic phenomena Involving the Appalachian chain, the Sierra
Range, and the Coast Range.
Later geologists, such as Russell (1.o,
p. 21) and Merriam (26, p. 301.), have more or less supported LaConte's
theory by reporting fissures, or feeder dikes, In the Columbia River
basalts through which the lavas were expelled.
At least two such feeder dikes have been recorded In the thesis
area,
The best of these occurs along the northwest slope of Paddy
Creek (SE cor., NW Ic SE Ic, Sec. 16, 1. 7 S., Ii. 1.1. 1) where it cuts
ilmestones and shales of the Martin Bridge formation.
This dike
averages about 22 feet in thickness and trends N 10° W for a distance
of about 150 feet.
(NE cor., Sec
The second dike is exposed along Goose Creek
, sec.
This
14, 1. 7 5., R. 43 E) in a recent road cut.
dike also cuts the Martin
rI.dge formation, has a northeasterly trend
and averages about 75 feet ln width.
Determiration of the dik&s
length is prevented by overburden.
Stretigraphic Relations and Age
Columbia River basalt unconformabiy overiles all other lithologic units with the exception of the Quaternary unconsolidated
deposits in the thesis area.
The thickest exposed section of these rocks occurs In the northeast corner of the thesis area near øoulder Creek,
in this locality
the basalts are relatively fiatlying and are estimated to exceed 1000
feet.
The Columbia River basaits are Middle Miocene In age.
In the
John Day Basin the basalts unconformably, overlie the John Day forma-
tion, the upper portion of which is Eower Miocene (27, p. 193).
in
the SBC area the Columbia River basalts are unconformably overaln by
the Mascall formation which is Upper Mlocene (27, p. 197).
UNCONCOLI DATED DEPOS ITS
Unconsolidated deposits of the thesis area comprise terrace
gravels and alluvium.
Both terrace and alluvium deposits are shown
on the geologic map and were distinguished In the field largely on the
basis of occurrence and degree of weathering.
in a few locations,
however, particularly in the northwest corner of the thesis area
along East Eagle and I agle Creeks, reworking of earlier terrace
materials with later alluvium has rendered the distinction end loca-
tion of contact less accurate.
Terrace Deposits
A terrace at en elevation of about 1,000 to k200 feet Is typically formed on the east sides of Eagle and East Eagle Creeks In the
northwest corner of the thesis area. Smaller and
s typical terraces
occur on the west sIde of Eagle Creek near the middle of the thesis
area at corresponding elevations. These terrace deposits consist of
inperfectly stratified silt, sand, graveZ, an boulders; are fair to
well sorted; and accumulated In beds characterized by wide variations
In the coarseness of the sediment. Soil horizons are generally lackIng and where found are lninature and s*ldcm thicker than 12 to 1k
Inches.
The princIpal rock types include quartz diorite, conglomerate,
basalt, greywecke, greenstone and limestone In decreasing order of
abundance.
Al though all rock types may be found wi th dl ne te rs of 12
Inches or less, materials in the range of 12 to 2k Inches tend to con-
sist of basalt, and those greater than 2k Inches to consist of quartz
diorite or conglomerate. DecoosItIon of the materials is characterized by surface oxidation and the development of Iron oxde stains,
spheroidal weathering, or the development of weathering rinds is
typical of larger materIals. Degree and depth of decay Is more extreme on terraces lacking good drainage and supporting a rich forest
vegetatIon.
The principal mineral constituents of the sand fraction in
dude feldspar, biotlte, quartz, chart and magnetite; accessories are
ilmenite, rutlie, apatite, and zircon. MI constituents are angular
or subangular, have poor sphericlty, and retaIn portions of their
original crystallographic form. Mechanical analysis show that
granules and pebbles (2.0 to 64.0
me) are the principal grain sizes
of the terrace materials. Cumulative frequency curves show (Figure
13) that the median dlaneter of three sIes from the terrace de'
posits on the east sides of Eagle and East Eagle Creeks and from the
deposit between Torchlight and Empire gulches are 3.25, 3.58, and
2.65
me
respectively.
Accumulation of the terrace materials Involved fiuviatile
transfer from a source not far removed from the site of deposition.
We))rounded cobbles and boulders and the comeon occurrence of bouI
den 4 to 8 feet in diaeter Indicate that the strean transporting
these materials had a discharge somewhat greater than the present
discharge of Eagle Creek. The presence of an unusually high sIit
clay content Is believed to be more indicative of postdepositional
weathering than any variation In the transporting strean's gradIent
or discharge.
Previous writers
(43, p. 20; 38, p. 57; 22, p. 585) have
indicated that many of the unconsolidated deposits In the Wal Iowa
Mountains are glacial in origin or are derived from glacial deposits.
Evidence supportIng this generalizatIon for the terrace deposits
100
90
80
/v7
70
I
z60
I-
'4,
Id
U
j
50
-40
I
0
Id
30
_
__
"0*
7, /
/
/_____
J
I
0
CURVES
_ _
UNCONSOLIDATED
/
FOR
DEPOSITS
/
20
I0
064
CUMULATIVE
_______
I
32
16
8
4
2
DIAMETER
1/2
I
IN
1/4
1/8
1/16
/32
1/64
1/128
MILLIMETERS
Figure 13. Cumulative size frequency distribution curves for unconsolidated deposits
1/256
82
described her. is inadequate end the writer doubts that these deposits
c
be psitIvelv correlated with any known glacial or Interglacial
stage.
The problem of correlation with glacial origin has, nevertheless,
proved an interesting one and certain relationships, although incon*
ciusive In themselves, deserve coement.
There Is no evidence, stratigrephical, *tructural, or geomer1.
phologlcal, Indicating that a glacier ever extended Into the thesis
area.
A short distance to the north, however, proof of glaciation Is
widespread md is characterized by such striking features as angular
peaks or horns, serrate ridges, ci rque basins and lakes, and U"eheped
valleys.
In the East Eagle Creek valley, epproxlmately 3 mIles north
of the thesis area at an elevation of about 41.00 feet, en
accumuie
tion of nonstratlfl,d glacial material measuring over 1000 feet in
length and roughly 100 feet In thickness may be seen.
This elongated
body Is undoubtedly the remnants of a lateral meraine deposited during
the last glacial stage.
The clos, correlation of elevation for this
merainal deposit with that of the terrace deposits in the thesis area
gives a slight hint of genetic significance. The correlation in It-
self, hver, cannot be used as definite proof as there Is no .epp.
able connection between the t
deposits.
Smith and Allen (1e3, Plate 1) have shown a glacial deposit on
theIr gologlc mep at an eløvation of
proximately 1.600 to 4100 feet
rj1
on the east
ide of Eagle Creek about a mite north of the thesIs are..
This deposit, if actuliy of g1c1al orlgln, represents te southern
most extension of active glaciation in this particular portion of the
southern WaI)owas
The deposit, like that on East Eagle Creek, Is
also at an elevation correspcndtng to those of the terrace deposits
in the thesis area and ry well have been the source from which the
materials of the terrace deposits were derIved.
Thicknesses of the terrace deposits are Inferred on the basis
of mining excavations and InterpretatIons from the geologic map.
U. U.
,ods1 has Informed the writer that a 5O-foot shaft was sunk
In the terrace materials near the mouth of O'Brien Creek In an attm,t
to reach the reportedly rich auriferous gravels lying on and dl rectly
above bedrock.
AssirnIng that badrock would have bean reached within
another 50 to 75 fcet
s suggested by other excavations less than
1/4 mile down Eagle Creek, and Including approximately 170 feet of
terrace materials overlying the collar of the shaft (as exposed on
the sides o1 O'Brien Creek), a total thickness of 270 to 295 feet is
obtained.
The method Is, of course, subject to error depending on the
depth of bedrock from the bottom of the shaft, but the figure given
is probably close to a minimum.
A maximum thickness estimate is
obtained by projecting the slope of the bedrock surface exposed on
the rock divides.
This method Is subject to possible serious errors,
WilJianW. Woods, Prospecter.
Richiand, Oregon.
F,,
especially thos* introduced by the flattening of the curve by whIch
bedrock surface declines toward the middle of the valley.
probable maxlm
The
thickness is about IIOO feet In the northwest corner
of the thesis cm as determIned near the dIvide between 0'$rlen and
Badly Creeks.
The age of the terrace deposits is probably early Quaternary.
Aliuviwe
Recent deposits of unconsofldeted materials occur along the
stre
courses of Eagle end East Eagle Creeks and along some of thel r
trIbutarIes,
The deposits range In texture from silt to boulders and are
cooperatively thIn, mostly less than 20 feet thick, except near the
mouth of Torchlight Cuich and In the smell basin near the head of
Little Eagle Creek where thicknesses are estimated from the geoiogc
map to be 150 and 300 feet respectively.
Bedding planes ar, well
defIned In same of the thicker deposits along Eagle Creek, but in
other pieces such structures are poorly developed or are absent.
Compsitions of materials are Identical with those of the ter
race døposits, the only significant difference being the absence of
large quantities of hydrous Iron oxides.
Cobbles and boulders are
well rounded and have geod spherlctty but with decreasing size
classes these textures are replaced by angular particles with poor
iphericity.
Th. degree of sorting, however, shows an appreciable 1n'
crease with decrease In size classes.
Th. principal difference In the grain-size distribution of
these deposits from those of the terrace deposits Is that they are
more sandy.
Mechanical analysis of the alluvium show a greater
quantity of send in the 2.00 to 0.12 me grain sizes.
CumulatIve fra
quency curves show that the median diameter for three samples, one
collected approximately 250 feet north of the East Ca1eEagle Creek
confluence on the west side of Eagle Creek, another from the west
side of Eagle Creek approximately 150 feet north of th
confluence, and another from the east side of E*gl
Paddy Creek
Creek approxi
rnately I/k of a mile north of tne Little Eagle Creek confluence,
are
1.45, 1.14, and 0.35 me respectively) as shown In 1igure 13.
Accumulation of the alluvial deposIts Is referred to the latter
part of tne Quaternery.
More recent deposits are found only near the
mouths of tributary streams where there Is a sharp decrease in stream
gradient or in small basins.
Structure
periods of deformation: (1) post-Triessic, pre*Creteceous deformation
which involves folding 0f the Upper Triassic sediments and thrusting
of the Permlan greenstone, and (2) post4iidd1e Miocene, pre-Plelsto
cane deformation.
SUg- as Trasslc, Upper than older is granite albite the If
1). Plate (8,
Creek Clover and
1)
Plate (6, Creek balm
a1og
folds the by suggested
as active been have may couple, horizontal a of result the or direct
either force, coaress1onaJ a that Indication some is there however,
quadrangle, Baker adjacent the in
thrusting. pre'Cretaceous Triessic,
poste by produced shearing extensive by defaced been have structures
such define might
cli hl
detected not were Folds
planes reference all as tone greens the in
strata. Trlassic Upper than metamorphosed
more much clearly Is greenstone Creek Clover PermLan the that basis
the on proposed tentatively is orogeny the area thesis the In
61).
p.
(38, Ross by Mountains
Wallowa the of portion southern the In established tentatively and
2)) p. (6,
Gilluly by quadrangle 8.ker adjacent the in established well
fairly been has orogeny Triassic pre-Upper post-Permian, A
DEFORMATION TRIASSIC PREØUPPER POSTIPERMIN4,
stock.
Cornucopia and bathoUth Weilowa the of eqlacemant acconanying
deformation Cretaceous Early en (2) and granite albite end greenstone
Creek Clover the affected apparently whicn oroeny Triassic. Upper
pre- post-Permian, a (i) inclide deformation of periods Other
thesis
srnafl
conclusIve
area.
relatively the In lacking Is movements tese for evidence
1(d50),
p. 5,
20; p. 13, 61; p. (38, Mountains low. Wa) the
near and in place took movement earth of periods other Aithotigh
gested by the occurrence of albitegranite"lIke pebbles In the Lower
Sedimentary series, then It Is possIble that the post-Permian, pre"
Upper Triassic orogeny played a major role in
the
athitization and
silIcificatlon of the quartz"dlorlte from WhIch the aibite granite
was derived.
POST-TRIASSIC, PRE"CRETACEOUS DEFORMATION
Most structural features of the thesis area are the result of
a post-Triasic, pre"Cretaceous orogeny.
features exposed in the thesis area were
Two major structural
produced
during this oro"
genic cycle: (I) great asnetrical folds which characterize the
Martin Bridge and Hurwal formations, and (2) thrusting of Permian
greenstone over UpperTrlasslc strata.
A complete description of the major folds exposed In the thesis
area is beyond the scope of this report due to Incoa lete exposures
and the complexity of structure produced by superimposed crenulatlons
and later earth movements.
folds are predominant.
It is probable that similar and isoclinal
The regional trend is northwest with a slight"
ly Increased westerly swing near the northwest corner of the thesis
area.
A shallow (5 to 100) northwesterly plunge is also apparent.
The thrusted na
of greenstone, located in the southwestern
portion of the thesis area, Is referred
to here
as the Empire thrust.
Structural relationships of the thrust may be observed to advantage
from a point
prox1mately 1/2 mile south of Basin Creek along Eagle
Creek as far northwest as Torchlight Gulch where the greenstones are
concealed by Tertiary lava.
Recognition of thrusting Is based pr1
marl ly on the fact that the rocks of the thrusted mass are greenstones
and that they are older than the rocks which they overlie (1, p. 183).
Evidenc
supporting this Includes petrographic proof that the older
rocks are greenstones and not an Intrusive flne'grained marginal
phase of the albite granite as formerly believed (38k p. 47).
Field
study has revealed extreme shearing In the greenston. near the thrust
contact with younger rocks; also, the gr-eenstone has been traced
without interruption from Its northern exposure in the thrust shet
southward to rocks exposed near the Little Eagle Creek confluence
which have bean correlated (38
p. 2
stone in the Baker quadrangle.
Small outliers, or kllppe were
with the Clov*r Creek gre.n.
mapped approximately 112 and 314 or a efle northeast of the thrust
margin and their occurrence may Indicate the general limit of th.ruit*
ing In that direction.
The only other thrust fault In northeastern Oregon recorded in
the lIterature is the Bayhorse overthrust (24, p. 36) which has been
traced from Burnt River, Oregon, northeastward to Cuddy Nountain,
Idaho.
This structure cuts Jurassic sediments and In places Is con
ceded by Coluebla River basalt.
EMIX CRETACEOUS NF*MT ION
Deformation of the older rocks as a result of granitic eapIacem
mont during Larly Cretaceous Is eore apparent In the high Wallow.is
than In the thesis area.
The local development of hornfe)sed grcen
Stone and Influence øf structural trends in the thesis area are
tentatively attributed to the emplacement of the Cornucopia stock.
PI$T4IIDDLE MIOCEME, P*E'PLEIflOCENE DEFORMATION
At some time after extrusion of the CohmbIa River basalt
and prior to the Pleistocene glaciation the area centering around
the present Wal Iowa Mountains began to rise.
The surrounding
basaltic plateaus were tilted and erosion began In earnest.
l.a the
thesis area the Tertiary levis are characterized by dips up to 30
degrees in many pieces, and al$hough the surface upon which the
levis were extruded was lrregular,meny of the steep dips resulted
from tilting produced during the uplift.
Faulting was undoubtedly
a principal defensatlonal feature In the region and It Is probable
that mest, If not all, of the major Tertiary faults in the Vallowa
Mountains wer. produced at this time.
No provable Tertiary faults were
recognized In the thesis area.
DOME.UKE STRUCTURE
In the north central portion
f the thesis area there is roughly
concentric distribution of roughly outward dipping strata surrounding
a central area of greenstone.
not rn..
The northern half of the structure was
, but a reconnaissance survey showed similar dIstribution
of strata.
As no positive reference planes could be determined in the
greenston., there Is some doubt as to what the dome-like structure
actually represents; three possibilities exist: (I) a dome, (2) an
outlier of thrusted greenstone, and (3) an interbedded volcanic unit
of the Lower Sedimentary
The best
series.
evidence favoring a domal structure Is the afore-
mentioned concentric distribution of lithologic units and
the
roughly
outward dIpping attitude from the central greenstone ucor& as revealed on the geologic map.
ranitIc rock occurring In small
Irregular patches, intrude the Lower Sedimentary series on the
north
and northwest flanks of the structure. Although there Is no definite
proof that granitic rocks underlie the rocks of the thesis area, it
is possible that the grani tic exposures represent small extensions
of a much larger Intrusive mass which may have produced an uplift.
The absence of extreme shear1n in the greenstone in the north
central part of the thesis area, such as characterized the greenstone
along Eagle Creek, seern to preclude the possibility of a thrust
origin, but admittedly Is not a conclusIve criterion.
The possibility that the greenstone is an Interbedded volcanic
unit of the Lower Sedimentary series was seriously considered during
field Investigations. However, no definite conclusions could be
reached as to stratigraphic relation between the two lithologic units.
In the best exposures the contact was irregular and undulatory.
The
geologic map suggests the possibility of an unconfor able relationship. Microscopically, the greenstones are similar in composition and
texture to the Clover Creek greenstone exposed in the southwestern
portion of the thesis area, the only exceptions being the locally
higher grade of metnorphJsm and the presence of amygdules.
Mining Geology
The search and development of gold lode and placer deposits
has been and still is the principal mining activity along Eagle
Creek and Its drainage area.
Hi STORY
The mining history of Eagle Creek probably dates back to the
early 1860's, about the time Eagle City (now Sparta) became a local
center of population.
Llndgren (22, p. 739) notes that in 1869 the
area was known as the Cooster (presumably nam& after Tom Kooster
who discovered gold In Maiden Gulch about 1+ mIles south of the thesis
area (3, p
10) and that approximately 250 men were actively engaged
In placer operations.
A few years later, In 1873, the Sparta Ditch
was cocr,leted and the mining activity shifted southward to the gold"
bearing stream beds and gulches near Sparta.
Placer operations In
the Sparta district continued for about 15 or 20 years and a-e reported
(22, p. 77) to have produced about $158,000 In gold.
During this time numerous Chinese, who were formerly enployed
In the construction of the Sparta Ditch, were operating small-scale
placers on the gravel bars and terraces along Eagle Creek.
With the
exhaustIon of the Sparta placers, mining Interests again shifted nort
ward and in the late 1800's gold was discovered near the mouths of
Dixie, Bennet, and O'Brien Creeks and later near the confluence of
Paddy Creek.
As a result of these last discoveries, a small community
naiied Pleasant Point including several cabins, a salli, and a post
2-93
office was established near the East Eagle Creek confluence (15,
p. 13).
Smal1sae lode and piecer mining continued for the next
40 years until early In 1942 government regulations and shortages of
men and equipment forced the gold mines to shut down.
DESCRIPTION AND PRODUCTION OF MINES
Valid production data, at least In that portion of the Eagle
Creek minIng district covered by this report, are not availabla.
The information that could be gathered on workings whose nses are
known, or on the more Important workings whose nes could not be
discoveped, is presented in Table 8,
Placer
3
4
5
Badger MIne
f3rendal Diggings
Conundrum Cr. Mine
* See Figure l4 page 97.
Fissure veins
2
Ashby Copper MIne
Fissure veins
Disseminated
I
Fisswe veins
Tve of Deposit
Amalganated Mine
LocaiIt
i4tber
Data on mines and prospects of thesis area.
Mine or Proset
Table 8.
Gold?-quartz veins, 3-6" wide) In sheared
conglomerate of Lower Sedimentary series.
Recent excavation.
Gold-bearing placer deposits in unconsolidated uatornary gravels. Operated in
early 1900. includes 3 miles of ditch.
Gold-bearing quartz veins in conglomerate
of Lower Sedimentary series. Underground
workings inaccessible.
Principal copper minerals Include chalcopyrite, bornito, and native copper. 40foot 20x20 shaft, 60-70' open cut. Present
owner (1957) George Ashby, Richiand, Ore.
owfler Nadine Strayer, Baker, Oregon.
Gold-bearing quartz vein 6lSU wide in
conglomeratic unit of Lower sedimentary
Series, 0O50O feet underground workings, 100-ton Huntington mill, two cabins.
intermtttnt operatIon 1900-1959. Present
Table 8.
ContInued
Mine or Pros*ect
Locality
Mumter
1e of Deposit
nts
Dolly Vardin
6
FIssure vins
Gold-bearing quartz veins. Tunnels inaccessible. Several open pits, some
recent excavations. Mint reports credit
this locality with a production of
$115,000 (22, p. 739)
Gold Eagle Quartz
Claim
7
Fissure veins
Gold and other minerals (?) In sandy
fades of Martin 8rfdge formation.
Open pIt, 2 miles of ditch. Owned
by Jess N. Thompson.
Lily White Mine
8
Fissure veins
Gold-quartz veins In liurwal ? formation.
Tunnel inaccessible. Reported 3aO1+OO
IncUne shaft. Abandoned.
Lower Eagle Placers
9
Placer
A group of placer mines along Eagle
Creek about 1.5 miles below Paddy Creek
confluence. Abandoned.
McGee MIne
10
Fissure veins
Gold-quartz veins. In Lower Sedimentary
series. Tunnel inaccessible. Abandoned.
Packsaddle Creek
Mine
ii
Placer
Gold-bearing alluvium of Recent origin.
ApproxImately 150-200 feet of open cut.
Pinehurst Mine
12
Fissure veins
Gold and copper in greenstone.
early l92Os. Abandoned.
Operated
Continued
13
14
15
Whittaker Mine
Woods Diggings
Locality
Njnber
Smith Diggings
Mine or ProsDect
Table 8.
Placer
Fissure veIns
Placer
Type of DeDostt
Recently developed workings (1958-59)ln
unconsolidated gold-bearing Quarternary
gravels. Work to date Includes approxlmately O feet of tunnel with steel track.
Recovery of gold In sluice box and hand
panning. Owner U. 11, Woods, Richiand,
Oregon.
Gold-bearing quartz veins In conglomer
ate of Lower Sedimentary series. About
100 feet of tunnel and shaft. Recent
Improvement.
Gotd-bearing Qua ternary gravels near
confluence of test Eagle Creek. Tunnel
and open pit workings. Abandoned.
orent
'S
3
II
U
-4
I4
8
20°,A
p
I
I"
4
ICh
I2
0
I
Figure 1k1
/
NLE$
Index map showing mining locations and distribution.
to
Historical Geology
Durtng the Permian the region was Included In the eugeosynclinal
belt that extended from Alaska to CalIfornia (17, p. LiO) and which in
northeastern Oregon received great thlckness of marine volcanics,
graywacke, limestone, shale, an.d chert which constitute the Clover
Creek greenstone. The relationships between th. lava flowS and
associated sediments are not preserved In the thesis area, but the
sane strata occur in the adjacent Gaker quadrangle (8, p. 88) in con
formable succession, thus eliminating any great Intervening period
of uplift.
A pre4ipper Triessic orogeny in the thesis area Is tentatIvely
proposed on the basis of the pparent)y greater degree of metamorphism
of the Clover Creek greenstone and albite granite than In Upper
TriessIc units.
Very little Is known regarding the Lower and Middle Triassic in
eastern Oregon.
Sediments may never have been deposited or If d
posIted, the strata have not as yet been recognized or are still con
cealed.
The Lower Triassic has been fairly well established in Idaho,
however, and according to Kumeel (19, p. 165) the section In the
southeastirn part of the state is one of the thickest irnsr Triassic
marine sections in the world.
During the Upper Triassic the region was submerged In a shallow
sea and received a great thickness of graywacke, conglomerate
lime
stone, chert and shale which coopose the Lower Sedimentary series.
Direct volcanic contributions were few as interbeddsd lives are absent
in the thesis area and found only In sparing amounts In adjacent
areas (38, p. 27). The source area from which the sediments ware
derived may have lain to the east of the thesis area as suggested by
the greater thickness of the sediments In that dIrection (38, p. 29).
The highly angular constituents of graywacke and the high content of
unstable feldspar and rock franents suggest that the source area was
characterized by considerable, perhs mountainous, relief and that
climatic conditions were
humid
continental with cool suomiers, thus
favoring physical rather than chemical decoosItlon of a predominantly volcanic bedrock. Th. occurrences of conglomerate throughout the
Lower Sedlmentary series suggest that crustal disturbances were more
or less Intermittent throughout the depositional period. The inter
bedded limestones were probably deposited during the 4uieter periods
and their occurrence Suggests that the shallow sea may have been
characterized by warm water currents that favored the precipitation
of caician carbonate. Deposition of the Lower $.4lmentary series was
terminated by a change In the sedimentary envlronment which Involved
a switch In the type of rock
dacoepositlon from predominantly physical
to chemical processes.
The caicareous deposits of the MartIn Bridge and Hurwal forma'
tions were accumulated in a warm, shallow sea that favored an
abundant
fauna) assemblage. The I Irnestone and shaly fades of these format Icns
have yielded a variety of pelecypods, gastropods, crinoids, and corals
which are known to favor ma,dmum development In the epineritic zone of
the marine environment. Deposition of the two conformable formations
Is known to have continued Into the uppermost Triassic (Rhaetic),
accumulating some $000 feet of limestone, shale, stndstone, mudetofte,
and conglomerate.
A shallow sea covered mest of Oregon and Washington during
Early Jurassic and the sediments deposited consist of normal sandstone,
shale, and limestone that are similar to the underlying sedimentary
rocks of Late Triassic age (16, p. 103).
regarding the Jurassic In the thesis area.
There is little information
var, a fossil collec.
tion made by the writer about a mile west of the thesis area near
Sanger gulch was regarded by Muller1 as consisting of anmonites whose
"coarse ribbing and evolute coiling make it possible that they repre
sent ir1.tItas-lIke forms" of Lower Jurassic or Sinemurlan age.
The
stratigrephic relationship between the "Lower JurassIc's and Upper
Triassls strata was not determined du
to the presence of concealing
Coluabis River basalt.
Qe of th. greatest orogen.ic periods, for which there Is a
clear record in and near th. thesis area, coomenced in the Jurassic.
The earliest effects of the orogeny were characterized by folding and
sheaFlng of the older rocks.
As the ultimate strength of the rocks was
gradually exceeded, rupturing took place and it was during this stage
that the Clover Creek greens tone was thrust over the younger calcareous
units of the M*rtln Bridge formation4
$lmon V. Muller, Professor, Stanford UnIversity.
Jun. 8, 1959
Emplacement of the Wsl)owa Batholith and Cornucopia stocks short
dIstance north of the thesis ares occurred during post'Cafloviasi. pr.
A)blai time (I6, p. 127A).
Although there Is no absolute proof of
uplift during this period In th. thesIs ares, It is reasonable to assums that forceful erqiacemcnt of the Wallows batholith (1+5, p. 1650)
was accompanied by deformation and a general raising of th. land.
The
region was probably of mountainous relief during L..t. Cretacious (9,
undergoing extensive erosion.
p. 573)
Almost nothIng Is known regarding the early Tertiary history
of the thesis area.
erosions
It Is probable that the land was still undergoing
as In western Idaho (39
reduced in elevation.
p. 31+), and that the thesis area was
At some time prior to extrusion of the Colia
River basalt, perhsq,s during Late Locene (38, p. 73), the region was
again uplifted and valleys were cut In the plateaus surrounding the
Wallows Mountains.
During the Middle Miocene, the region was covered by Columbia
River basalt.
In the thesis area en erosion surface of moderate re-
lief was completely concealed by fissure-erupted lava flows whose
aggregate thickness probably exceeded Z000 to 3000 feet.
BasaltIc
feeder dikes are not conspicuous In the thesis area, but in the hIgh
Wailowas they stand out In striking contrast to the light-colored
grard tIc rock which they transect.
102
,.
Figure 15. Two basaltic feeder dikes are shown
cutting granitic rocks of Cornucopia Peak.
(Eagle Meadows shown in foreground)
Uplift of the present Wal Iowa Mountains occurred during the
Pliocene.
The basaltic plateaus surrounding the mountains were
tilted, stream valleys were developed, and all Tertiary lava was
eroded from parts of the area.
it Is generally concluded that the Pleistocene in the Wallowa
Mountains began with the coming of glaciation (38, p. 7k).
The
effects of this epoch, although grandly displayed in the Aipinelike
mountains of the high Wallowas, are not well preserved In the thesis
area.
It Is doubtful that any active glacier extended farther south
than 2 to 3 miles north of the East Eagle Creek confluence; some of
the terrace gravels below this point, however, may represent outwash
beyond the melting glacier.
Livingston (23, p. 705) has suggested
that great quantities of gravel were carried down Eagle Creek when
the glacIers were melting at the close of the Pleistocene, and that
the materials were deposited In the form of an alluvial fan which
completely blocked the Powder River in the vicinity of Eagle Valley,
producing a large lake.
At the present time the thesis area Is undergoing erosion.
A
few deposits of unconsolidated materials are accumulating, but these
are restricted largely to small basins at the head of stream courses
and other relatively flat areas.
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