GEOLOGY OF THE SOUTH'ESTERN PART OF EAGLE CAP
)UNTAINS, OREGON
QUADRANGLE, WALLOWA
by
GARY LEON CARNAHAN
A THESIS
submitted to
OREGON STATE UNIVERSITY
in partial fulfillment of
the requirements for the
degree of
MA.STER OF SCIENCE
June 1962
APPROVED:
Redacted for Privacy
In Charge of' Major
Redacted for Privacy
ieaa of
Redacted for Privacy
Chairman of Schdol Grad!ate Committee
Redacted for Privacy
Dean of Graduate School
Date thesis is presented
Typed by Betty Anderson
Jiiô1 2S, /9I
ACKNOWLEDGEMENTS
The writer wishes to express his appreciation to Dr.
J. C. Cvmmings, his major professor, for assistance and
guidance received during the preparation of the manuscript.
The writer is grateful to all of the faculty for ad-
vice and suggestions concerning the thesis, to Dr. Ira S.
Allison for his critical review of the manuscript, and to
Dr. J. V. Byrne for his critical review of the sedimentary
units.
The writer is grateful to Dr. W. H. Taubeneck for
assistance and guidance received during the field and laboratory work, and for criticism of the manuscript.
The writer is grateful to Dr. S. W. aller of Stanford
University for his identifications of the fossil material.
The writer's wife, LaVerne Carnahan, deserves special
ance with typing and revision of the manuscript, plus many
other things too numerous to mention,
thanks for her companionship in the field, for her assist-
TABLE OF CONTENTS
I NTROIXJCTION
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S tratigraphy
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STRATIGRAPHICUNITS ................
Lower Sedimentary Series
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Provenance and Depositional Environment
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Greenstone Conglomerate Unit
Siltstone-Sandstone Unit . .
Stratigraphic Relations .
A go arid Fauna
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Martin Bridge Formation
Laminated Calcareous Siltstone Unit
Upper Limestone Unit
Thickness
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31f
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Environment
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A go and Fauna
Thickness
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Provenance and Environment
Me tasediments
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a
a
Lower Limestone Lentils
Greeristone arid Limestone Conglomerate
Lentils
Upper Limestone Lentils . . . . . . .
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21
26
0
a
Siltstories-?4idstonos
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15
15
a
a
a
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Age and Fauna
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Provenance and Depositional
HurwalFormation.
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a
a
a
a
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51
HilmmftigbirdMountain
........... 51
Forks Forest Camp - Upper Dixie Creek . . . 52
ColumbiaRiverBasaits
Petrography
Structure
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Stratigraphic Relations
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Thickness.
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Ago
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57
57
a
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MethodofExtrusion. ......... ..
60
QuaternaryDeposits ..a..aa.a.aa..
61
Table of Contents (cont.)
PaRe
INTRUSIVE UNITS
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67
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QuartzDiorite...,.,,...,
Age
Gabbro ,
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GEOI'KRPHOLOGY
GlacialForms
NonglacialForms
...se.....a ...
1
70
STRUCTUR.ALGEOLOGY0.....a.a.......
72
HISTORICALGEOLOGY.
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76
.............,..
79
ECONONICGSOLOGY
BIBLIOGRAPHY
APPENDIX
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86
LIST OF FIGUIES
Figure
Page
3.
Index map showing location of thesis area
2
Greenstone conglomerate of Lower Sedi-
3
.
2
mentarySerias...............
9
Laminated siltetone of Lower Sedimentary
Series . . . . . . . .
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17
Load cast in siltetone of Lower Sedimentary
Series . . . . . . . . . . . . . . . . . .
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17
Laminated caloareous siltstone unit of
Martin Bridge formation . . , . ...
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19
Laminated calcareous siltstone grading into
massive limestone of Martin Bridge formation
20
7
Marble of Martin Bridge formation
*
20
8
Drag folds in bedded limestone of Martin
.... .......
28
i
5
6
Bridgeformation...
9
Slaty argilhite of Hurwal formation
11
l+
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28
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38
Laminated siltstone-mudstone of Hurwa]. formation
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38
Greenstone conglomerate lentil in Hurwal
formation .
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a
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13
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Close-up of drag folds in bedded limestone
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Close-up of greenstone pebbles
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a
a
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a
Limestone-greenstone conglomerate lentil in
Hui'walformation.....,...,.,.,
1f3
15
Contorted limestone lentil in Hurwal formation
)+3
16
Edge of' Columbia River basalt flow
55
17
Basalt feeder dikes in batholith
18
Lateral moraine at base of NwrnLingbird
Mountain a
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EastEagleValley
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a... a ,aae. .
a
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68
68
LIST OF TABLES
pare
Table
1
2
Swninry of Stratigraphic Units
Size Distribution of Pebbles in the Greenstone
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glomerate
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4
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Composition of the Lower Sedimentary Series:
4
5
Siltstone and Sandstones
Composition of Calcilutite
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6
Composition of Calcareous Biltstone .
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7
Composition of Calcareous Sandstone
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10
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11
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13
a
23
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23
...........
CompositionotMarble
9 Composition of Bedded Limestone
8
4
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S
S
U
12
Composition of Siltstones arid 14.idstones
13
Composition of
11+
Composition of Hurwal Formation:
Cobble Conglomerates
a
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30
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31
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33
*
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1+0
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+0
Granule and
e
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1+1+
*
a
a
15 Composition of Upper Limestone Lentils
16 Composition of Columbia River Basalt
17 Composition of Quartz Diorite .
25
25
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Lentils
the Lower Limestone
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*
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Composition of Limestone Conglomerate
Composition of Greenstone Conglomerate
10
6
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ConglomerateUnit
3 Lower Sedimentary Series Greenstone Con-
1+
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1+6
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58
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65
LIST OF PLATES
Page
Plate
1 Correlationchart.,.............
5
..... .. . ......
88
2
Photomicrographs
Fig. 1
Fig. 2
Fig. 3
Fig.
3
Gritty sa ids tone of Lower Sedimentary
Series
Lamina bed siltstone of Lower Sedimentary
Series
S
Marble of Martin Bridge
:
:
Marble of Martin Bridge formation . .
;0;0 :
Photomicrographs
Fig. 1
Fig. 2
Fig. 3
Fig. L
siltstone of
Laminated calcareous
Martin Bridge formation . . . .
Bioclastic limestone of Martin Bridge
formation . . . . . . . . . . . . .
Calcilutite of Martin Bridge formation
Limestone conglomerate of Martin Bridge
formation . . . . . . . . . . . . .
Photomicrographs
Fig. 1
Fig. 2
Fig. ?
Fig. '
. ... .. . . .. . . ... 90
.......... .... .
92
Calcareous pellets from lower limestone
lentil of Hurwal formation . .
Bioclastic limestone of Hurval formation
Marble of Hurwal formation
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Marble of Hurwa]. formation .
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. .. .
. . . . . . . .
SPhotornicrographs . . .
Fig. 1 Bioclastic limestone of Hurwal formation
Fig. 2 Calcareous pellets from Upper limestone
lentil of Hurwal formation . . .
Fig. 3
Fig. +
6
Granule limestone and greenstone conglomerate of Hurwal formation . . .
Granule greenatone conglomerate of
Hurwalforznation
Photomicrographs
Fig. 1
Fig. 2
Fig. 3
Fig. +
. . . . . . . . . . . . . . . .96
Laminated siltstone of Hurwal formation
Laminated siltstone of Thirwal formation
Microfaulting in siltstons of Hurwal
formation . .
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Argillite of Hurwal formation . . . .
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LIST OF PLATES (cont.)
Plate
7
Page
Photoaicrographs
..... ... .......
98
Fig. I Porphyritic Columbia River basalt
Fig. 2 Aphanitic Columbia River basalt . .
Fig. 3 Myrmekite in quartz diorite . . .
Strained quartz in quartz diorite .
Fig.
8
Geologic map
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99
GEOLOGY OF THE SOUTRb4E8TERN PMIT OF EAGLE CAP
QUAIR&NGLE, WALLOWA MOUNTAINS, OREGON
INTROIXJCTION
The purpose of this thesis is to delineate the structure and stratigr'aphy of Triassic strata in an area of 52
square miles in the southern part 0± the Eagle Cap quadrangle, Oregon.
The thesis area is located between 1f 5° 00' and f5
05' north latitude and 117° 20t and 117° 30' west longitude
(Figure 1).
The area is 23-33 miles northeast of Baker and
7-15 miles east of Medical Springs,
The area is accessible over a good semi-improved logging road from Medical Springs and by roads along Eagle
Creek and East Eagle Creak.
Field work was carried out in thirteen weeks from
June 1
to September 15, 1959.
The U. S. Geological Survey
topographic map of the Eagle Cap quadrangle was used as the
base map.
Geology was plotted at a scale of 1/20,833 on
field and final maps.
Laboratory work consisted of the microscopic examination of 130 thin sections, preparation of 60 insoluble
residues and 30 acetate peals, and the determination of
roundness and sphericity for two conglomerate sets.
Modal
analyses were made by a point counter and Wentworth Stage.
Plagioclase was determined by Michel-Le 'vy 's chart (9).
1. H
3
Only three published reports are devoted to any part
of the thesis area.
For a report on gold mining in north-
eastern Oregon, Lindgren,. .)90l, (17) made a pioneer survey
along Eagle Creek and East Eagle Creek.
As part of a gen-
eral study of the southeastern Wailowa Mountains, Ross,
1938, (27) included five square miles of the thesis area.
Smith and £Llen, 19+1, (30) made a rapid survey of the
area as part of a report on the northern Wallawa Mountains.
The northern border of the area is mountainous, but
the central and southern parts are a dissected plateau.
The maximum relief is +,3iO feet, and the maximum elevation
is 8,36k feet.
Nearly radial drainage has developed on the central
plateau, with the topography in a stage of late youth.
Vegetation is thick in the southwest and western portions of the area, and is extremely dense along many creek
bottoms.
The thickest underbrush consisting of huckleber-
ries in a stand of closely spaced lodgepole pine is west
of Bennet Peak and east of the confluence of Two Color
Creek with Eagle Creek.
Rock is generally well exposed along valley walls and
in some creek beds.
Road cuts along Eagle Creek in the
southern part of the area and roads to the mines above
East Eagle Mine made excellent exposures.
if
STRATIGRAPHY
The Wallowa Mountains contain a thick section of sedimentary arid volcanic rocks ranging in age from Permian
through Tertiary.
In the thesis area; however, only Upper
Triassic sediments and younger igneous rocks are found.
Sedimentation was apparently continuous from the
Karnian Stage to the Norian Stage because interruptions in
sedimentation were riot found among the three Upper Triassic
formations.
Argillaceous rocks of the Rurwal formation
conformably overlies the limestone of the 4artin Bridge
formation which in turn lies conformably on the argillaceous
and conglomeratic sediments of the Lower Sedimentary Series.
The following local correlation chart was compiled
from Smith and Alien (30, Wethereli (37), and Prostka (26).
5
CORRELATION. CHART
Period
Sm:lth and
Allen (30)
Area
and
Tertiary
Columbia
River
basalt
(37)
Qal
Qal
IllullIltillI
III I!
I
I! I Ill
Qm
Qrn
Qrn
'1111111111 I III IT!
Wetherell
(26)
Qal
Qal
Quaternary
Prostka
Thesis
11111 liii l ii liii 11111 liii
Columbia
River
basalt
Columbia
River
basalt,
tuffs,
Rhyolitic
ii i
i I
i
ii 1TtT'
Columbia
River
basalt
dikes
IItii 11111 IFI1 III
Ur,rer
Triassic
FItfIllil liii
Hurwal
formation
Martin
Bridge
formation
Hurwal
formation
Martin
Bridge
formation
Lower
Sedimentary
Series
Lower
Sedimentary
Series
1II IlIllIllilI
Hurwal
formation
Martin
Bridge
formation
Lower
Sedimentary
Lower
Sedi-
w w
mentary
Series
Series
-
-
-
-
(Bottom
not
Lower and
exposed)
w
Northem
greenstaes
Mid die
I II III_
Imnaha
formation
Triassic
Permian
Clover
Creekgreen-
stones
Plate 1.
Elkhomn
Ridge
argil-
lite
Trinity
Creek
formation
Vertical lines, represent known unconformity.
Slanted lines indicate lack of information.
(Mid-Karnian)
Upper Triassic
Upper Trias sic
(Xarnian)
(Upper ICarnian
Norian)
Upper Triassic
Miocene
Quaternary
Quaternary
Lower Sedimentary
Series
Martin Bridge
Hurwal
Angular Unconformity
Columbia River
basalt
Unconformity
Unconformity
Thin-bedded siltstone, argilhites,
greenstone conglomerate, minor sandstones, and crystalline limestone
ates, marble
pyritiferous, calcareous siltstones,
limestone and greenstone conglomer-
Mxdstones, siltstones argillltes,
massive fragmental an& bioclastic
limestone. Greens tone and limestone conglomerate. Metasediments:
marbles, hornblende-biotite schi s ts
Argillaceous, carbonaceous limestone,
conglomeratic limestone; thin bedded
Basalt flows
Glacial deposits
Alluvial valley fill
SUMMPIRY OF STRATIGRAPHIC UNITS
TABLE 1
Variable
1000-1700'
])+00-2500'
ioO-68oO'
0-200' ?
0-2110' 9
Variable
0-1%' ?
STRATI0RAP1IC UNITS
L0R SEDIMENTARY SERIES
With the exception of black slate and those sadimentary rocks intercalated in the Clover Creek greenstones,
Ross (27, p.26) referred to all sedimentary rocks stratigraphically below the Martin Bridge formation as Carboniferous sedimentary rocks.
Smith and fln (30, p
8) des-
cribed the Lower Sedimentary Series in the northern Wallowa
Mountains as a group of shales, sandstones, and lenses of
limestone more or less altered to pyritized hornfels,
schists, and crystalline limestone.
In the northern Wal-
iowa Mountains these rocks reportedly underlie the Martin
Bridge formation unconformably.
Smith and Allen (30, p.
9) assumed that the Lower Sedimentary Series is equivalent
to the Carboniferous sediments of Ross,
The Lower Sedimentary Series occurs along East Eagle
Creek near the eastern boundary of the area and generally
strikes north-northeast parallel to the stream.
The rocks
are exposed continuously over three square miles, and
intermittently under a broken cover of alluvium and moraine
for another two square miles.
Rocks of the Lower Sediman-
tary Series are resistant to weathering, and where dis-
sected by streams, form steep slopes covered by massive,
bloc1y talus.
[.1
[SI
The term Lower Sedimentary Series used in this report
is divided into two units on the basis of different 11thologies:
(1) Greenstone conglomerate unit and (2) Silt-
stone-sandstone unit.
Both units are mappable and contain
several minor lenses.
The major units may represent inter-
tonguing of two thick beds.
ii 1J k)rWl
The thickest unit of the Lower Sedimentary Series
is the Greenstone conglomerate, extending from the extreme
northeast corner of the area to three-quarters of a mile
south of Jack Creek.
Petroraphv.
The coarse clastic unit is composed of peb-
bles and cobbles of altered volcanic rocks tightly packed
in a weli indurated, purple to green silty matrix (Figure
2).
The size of the clasts apparently increases from
north to south (Table 2).
conglomerates.
Sorting is poor in the coarser
!bst pebbles and cobbles are aubz'ounded
to rounded and less resistant rock varieties are well
rounded.
The finer atr1x material is generally sub-
angular.
Silicified greenstones are more numerous than other
rock types (Table 3).
These greenstones have a dense, re-
crystallized siliceous groundaasa with randomly distributed
phenocrysts of unidentifiable clouded plagioclase, possibly
--
1
..'lgure 2
ve11 Indurated polynictic cong1oerats
Gz'eenstone conglorierate unit
Lower Sedimentary Jerles
Location: ;E*NE eec. 29, T. 6
5., H. 14k E.
10
Table 2
DISTRIBUTION OF PEBBLES IN THE
OREENSTONE CONGLOMERATE
UNIT
SI
North
South
Creek South
of Jack Creek
Jack
Creek
Gold King
Creek
Hudson
Creek
280 mm.
60 mm.
20 mm.
10 mm.
Max. Clast
Size
Average
Size
albite.
3
mm.
O-15O common
Some textures in the greenstones appear trachytic,
but this is difficult to determine because of the alibiAndesites and basaits are found among the sill-
fication.
cified and non-silicified greenatone clasts.
Similar
material is found in the matrix of the conglomerate (Table
3).
Other less numerous rock types such as
granites,
schists, and marbles denote the heterogeneous nature of
the conglomerate.
Low grade metamorphism is partially responsible for
the induration of the rock.
Interstitial brown biotite,
chlorite, and epidote denote the greenschist fades (34,
3). Microcrystalline quartz, hematite,
also aid in the induration.
Thickness.
calcite and liaontto
The conglomerate is partly concealed by allu-
vium and glacial deposits, and so its thickness is unknown.
However,
near
the northeast corner of the area, the minimum
11
TABLE 3
LOWER SEDIMENTARY SERIES
GREENSTONE CONGLOMERATE
Greens tone
Very abundant
Material.
Ba salt a
Andesites
albitized
±silicified
Chert
Limestone
Common
Less Common
Less common
)bida tone- siltstone
Schiat
Granitoid
ReI e
Rare
c!
*
Greenstone rock fragments
Leucoxene
Limonite*
Chlorite*
Sericite
Biotite
Epidote
Hyper sthene
Quartz (8)
metamorphic
igneous
Oligoolase
Ore minerals
Magnetite
flaenite
Leucoxene
Microcrystalline quartz*
Calcite*
Hematite*
*Cementing agents
12
thickness of the conglomerate is estimated to be 1700 feet.
SiLts tone-Sands tone Unit
Purple to green siltstones and sandstones, rhythmically laminated and graded, are found only in the vicinity of
East Eagle Mine. These beds differ In attitude, strike
west-northwest, and disappear on the western slope of upper
Bradley Creek.
Petrogra.ph. The size range for the elastic material is
from 36 to 270 mIcrons.
ticles are
In some outcrops,
grit size
par-
2.5 mm In diameter (Plate 2, Figures 1, 2).
The siltstone-aandatones are texturally and compo-
sitionally immature as denoted by poor sorting and pack-
plus unstable mineral
spar (2k).
ing,
association of quartz and feld-
Induration of the ailtstone-sandstone unit is attrib
uted to low grade metamorphism of the argillaceous material.
Because of the sandstones containing more than 10 per cent
argillaceous material, 1t-0 per cent rock fragments, and 0
per cent quartz, these sandstones are lithic graywackas.
Thickness.
The thickness of the siltatone-sandatone unit
is difficult to
by folding.
estimate because of possible repetition
However, this unit may be as much as 1,000
feet thick in the vicinity of East Eagle Mine.
of the unit Is not exposed in the thesis area.
The bottom
13
TABLE
COMPOSITION OF TIlE LOWER SEDIMENTARY SERIES:
SILTSTONE AND SANDSTONES
Gi'eens tone Fragments
Andesites
asalts
-Albitized
3ilicified
Siltstonenazdstone
Limestone
Chert
Quartz (8)
Metamorphic
Igneous
Plagioclase
Altered
Ore minerals
Rutile
Magnetite
Limonite
Leucoxene
Serioite
Chlorite
Biotite
Epidote
Calcite
Hematite
Microcrystalline Quartz
Pyrites
Ilmeni te
Brachiopod or
Pelecypod fragments
(Genus and species undetermined)
*pyrlte is found only in the green siltstones.
Intra.-formatioxial elation.s
The upper part of the
Lower Sedimentary Series in the northeast corner of the
mapped area consists of greenstone conglomerate This relationship continues southward to Lime Creek.
Between
Lime Creek and Gold King Creek an interbedded series of
dark laminated siltstones, argil].ites, and limestone occur
in the upper part of the conglomerate unit.
These inter-
beds do not continue south of Gold King Creek.
The contact relationship between the greenstone conglomerate unit and the siltstone-sandstone unit is uncertain.
South of Jack Creek the conglomerate thins to the
southeast and disappears beneath alluvium before coming
into contact with the siltstone-sandstone unit.
Since
both units are conformable with the lower portion of the
Martin Bridge formation, they may have been contemporaneously deposited.
Inter-formational relations.
According to Ross,
(27, p. 29) and Smith and Allen (30, p. 8) the contact be-
tween the Lower Sedimentary Series and overlying Martin
Bridge formation is unconformable in both the northern and
southern Wallowa Mountains.
Along East Eagle Creek and
the adjacent area, parallel attitudes on either side of the
Lower Sedimentary Series-Martin Bridge contact suggest a
conformable sequence.
However, this does not exclude the
possibility of a disconformity.
S
15
Fauna
Fossils collected from the Lower Sedimentary Series,
according to Smith and Allen (3Q p. 9) are of an Upper Tn-
assic age.
Two fossil accumulations, fl.-21 and Fl22 were found
in the silts tone-sandstone unit by the writer and contained
external molds of indeterminable pelecypods or brachiopods.
Prcvenarice
Debositional Enyironment
Volcanic rocks, such as the Permo-Tniassic Clover
Creek greenstones were the source for most of the conglomeratic materials of the Lower Sedimentary Series According to Gilluly (ii-, p. 22) the Clover Creek greenstone
consists of quartz keratophyre, keratophyne flows and tuffs,
meta-andesite, chert, limestone, argillite, apilite, and
albite diabasos. Basement rocks, including metamorphics,
imist have been exposed in the region to account for the
schistos gneissic, and plutonic rocks found in the conglomerate.
Short transport and quick burial ar.e assumed for the
coarse elastic material because of the presence of limestone boulders. Limestone disintegrates over a long distance of abrasive transport (25).
Unstable rock and mineral assemblages, poor sorting,
and the thickness of the conglomerate suggest rapid deposition in a
subsiding trough near a local elevated source
16
area.
An eugeosyncline is characterized by this type of
deposit when associated with volcanic material (10, p. 35%
The siltatones and sandstones were apparently deposited from a imich reduced source area.
Turbidity currents
are assumed to have aided the transportation and deposition
of the fine clastic material, and also may have assisted
deposition of the conglomerates.
turbidity currents is:
Field evidence suggesting
(13, l, 15)
1.
Thick undisturbed bedded sequence
2
Repetitious bedding
3.
Sedimentary structures (Figures 3, 4)
Graded bedding
Load and flow casts
Convolute bedding
+.
Absence of ripple marks
5.
Absence of cross-bedding
6.
Absence of other small scale shallow water
structures.
Pyrite in the green siltstones and hematite in the
purple silts tones indicate alternating anaerobic to aero-
bic environmental conditions.
erally not found interchanged.
The two minerals are gen-
'iii cH
'.
\
Figure 3
Rhythinicall:, lwninzited and graded beds of
purple siltstone
Silts tone- sandstone unit
Lower Sedimentary Series
sec. 29, T. 6 S., 11.
Location; SW*SES
.1# 4[L_
'"!!
:1
.1
I
J' r
P
H?
Ij
1
-
/
Figure +
Srnn.11 load cast In ciltctone
Siltstone-sandstone unit
Lower Sedlirientary Series
LocatIon:
100 feet T'E of Fig. 2
E
MARTIN BRIDGE FORMATION
Smith (31, p. 9)+)
measured a
section of Triassic
"reefs" along Eagle Creek near Martin's Bridge, 6 miles
southeast of the thesis area. This area subsequently was
named by Chaney (2, p. #) as the type section for the
Martin Bridge formation.
formation are
three square miles of the Martin Bridge
present paralleling the west side of East
Eagle Creek.
Along the sides of the ridges the massive,
Approimtely
white to gray limestone is conspicuously exposed forming
steep slopes. The other calcareous rocks
Bridge formation are not exhibited in such
in the Martin
rugged exposures,
but have been weathered to a smoother topography.
In the thesis area the Martin Bridge formation consists of some 10 lenses
recognizable
which are thin and non-mappable
in outcrop
at the
thesis
few are recognized solely in thin-section.
most of
scale.
A
Basically the
compositions are very similar; textures, however, are extremely variable.
The Martin Bridge formation is herein subdivided
into two basic units and 10 lenses on lithologic and textural criterias
Laminated Calcareous Siltatone Unit:
1.
2.
Greenstone conglomeratic limestone
Calcilutite
I
Figure
LamixmteU cQ1coreou3 3iltstone woat1ertaC 1on
1cminze 1v1n the unit rt tha1r cppecrnce
tirtin BrldL;e iorrntion
Location:
1ThSE* soc. 29, T. 6 S., R. k E.
20
Figure (
Laminated calcareous slltstone grading into
overlying upor limestone unit
rtin Bridge formation
3W sec. 32, T. 6 8., R. +)+ E.
Location:
FIgure 7
Sacchcroi&l marble on the southeastern tip
of Grjnite Cliff
Upper lirnetone Unit
Mnrtln Bridge formation
Locationt sec. + and 5, T. 6 S., H. + E.
21
3.
L3,
Laminated calcareous siltstone
Caloareous sandstone
Limestono-greenstone conglomerate
Upper Limestone Unit:
5,
6. Marble
7.
.
9.
10.
Calcarenite
Bedded limestone
Limestone conglomerate
Greenstone conglomerate
For simplicity of description the various lenses
within the units wiU be discussed in their apparent
stratigraphic order.
jjg Calcareous Siltstone Unit
The laminated siltstone unit is distinguished by
a thick sequence of light to dark gray, rhythmically lami-
silts tone stratigraphically below the
wh Ite limestone. This unit is exposed south
nated calcareous
upper gray to
of Jack Creek in
the East Eagle Mine-Bradley Creek area
(Figures 5, 6).
Or ens tone
conglomeratic limestone. The greenstone
conglomeratic limestone is found at local intervals near
the base of the laminated unit south of Jack Creek in the
middle of sec. 29, T. 6 8., R +4 E. and in the SW+ sec. 32,
T. 6 8., R. 4-+ E.
The pebbles range from + to 50 mm in diameter. The
majority of pebbles are rounded to well-rounded and have
high ephericities. However, the finer clastic material in
the matrix is angular to subangular. A high ratio of
matrix to pebbles suggests poor sorting. Calcareous pellets
22
composed of fine-grained calcite are also present in the
matrix.
The matrix of this conglomerate is dominantly of calcite in contrast to the argillaceous matrix of the Greenstone Qonglomerate Itnit of the Lower Sedimentary Series;
pebble compositions, however, are similar.
Calcilutite.
A bedded calcilutite interfingers with
the Greenstone conglomeratic limestone and a thin-bedded
calcareous siltstone in the SE* sec. 29, T. 6 8., B. ifif B.
The calcilutite weathers yellow-brown in part, and is blueblack on a fresh surface.
Color differences are due to
the oxidation of pyrite along the bedding planes (Plate 3,
Figure 3).
The ca].cilutites are thin-bedded with beds
1 to 1f inches thick.
The average diameter of the calcite particles is 2
to 6 microns with a few larger particles 9 microns in diameter.
Algal structures as large as 22 microns in diameter
are present but uncozion (6).
Lmfnated calcareous siltstone.
A thick repetitious
sequence of laminated calcareous siltstone grades into the
overlying massive white to gray limestone in the SW see.
32 and SE * sec. 29, T. 6 8., R. 4k B. (Figure 6).
The
laminated sequence appears to overlie the conglomera tic
limestone and the calcilutite, but underlies the calcare-
ous sandstone and limestone-greenstone conglomerate in sec.
29.
23
TABLE
COlW0SITION OF CALCILtJTITE
Calcite (90 per cent)
Quar'
Blotite
Calcite
Magne tite
Clays ?
9gj
Material
Alga]. Structures (6)
Alga]. Dust (hi)
Carbonaceous Matter
AutJd2enic Minerals
Microcrystalline Quartz
Pyrite
TABLE 6
COMPOSITION OF CALCABEOUS SILTSTONE
Detrita].
Calcite
iartz
Clays ?
Material
Fossils
Discotroites sp.
Halobia SPe
Carbonaceous material
Alteration/recrystallized
Minerals
Ljinonjte
Pyrite
21
Abundant pyrito is present along the dark laminae
(Plate 2, Figure 1).
thick.
The dark laminae are 0.5 to 1.5 mm
Many of the light-colored laminae are coarser
grained and somewhat graded.
ceous material is abundant.
Fossiliferous and carbonaPelecypods and ammonites occur
along the lamination planes.
Calcareous sandstone.
This sandstone which is ap-
proximately 30 feet thick, is exposed one-half mile north
of East Eagle Mine and is also exposed two-tenths of a
mile south of the northern massive limestone in upper Bradley Creek.
A unique feature of this sandstone is the in-
clusion of saucer-shaped fragments of laminated siltstone.
These fragments, aligned with the bedding, are near 8 mm
thick by 35 mm in diameter.
Some are 50 mm in diameter.
Other detrital material is generally angular and
unsorted.
The rock is indurated by a partially recrys-
tallized calcite matrix.
Calcite has also embayed most of
the detrital material.
limestone-greenstone conglomerate exists below the massive
white-gray limestone and above the calcareous sandstone.
The clasts consist
of limestone and greenstone material
in a well-indurated silt-sand matrix of similar composition.
Sizes of the clasts range from 5 to 30 mm.
Composition of the conglomerate is similar to that
of the greonstone conglomeratic limestone.
However, the
25!
TABLE 7
COMPO$ITXON OF CALCABEOUS SANDSTONE
Calcite
Greenstone fragments
basalt?
Chlorite
Loucoxene
Limonite
Silt stone fragments
Quartz (8)
Calcite
Igneous
Metamorphic
Chert
Andes irte
Magnetite
tLcrocrystalline quartz
Hematite
J1
;L
COMPOSITION OF MABBLE
Calcite (96 per cent)
Magnetite
Quartz
Phiogopite
Chlorite
2.
notable difference between the two conglomerates is the
lesser amount of calcium carbonate interstitial cement in
the limestone-greenstone conglomerate.
Uper Limestone Unit
The upper limestone unit contains a variety of limestone types including marble, calcarenite, limestone con-
glomerate, and greenstone conglomerate.
)rble.
Thick bedded, white, saceharoidal marble is
prevalent in the northeast corner of the mapped area where
metamorphism associated with the emplacement of the Wa).-
Iowa batholith has caused recrystallization (Figure 7).
It consits of calcite grains 90 to 1f0 microns in size.
Most of the calcite grains are elongated with subparallel
plane or interlocking boundaries (Plate 2, Figures 3, +).
Fibrous and micaceous grains of clear chlorite and phiogopite occur interstitially. Heavy mineral separations of
an insoluble residue from the marble contained nearly 9
per cent phiogopite.
Deformed twinning
laameilae, elongation and inter-
locking boundaries are probably attributed to emplacement
of the batholith.
Calcareite. The massive limestone along Gold IUng
Creek (NE* Sec. 1.7 and SW* Sec. 32 T. 6 8. B.
E.) is a
fragmental limestone. This limestone type is recognized
only in thin section.
The fragments have a variety of
textures, and are separated in most cases by stylolites.
27
Fragments about 0,
to 2.0 mm in diameter consist of
vidual calcite grains 2 to 8
microns
pellets are 0.1 to 0)+ mm in size.
in diameter.
mdi-
Calcite
The length to width
ratio of the pellets is approximately 2:1.
also contains authigenic
hematite and microcrystalline quartz.
eded Limestone. Bedding is not apparent on the
This fragmental
limestone
weathered surface of all the upper liinestones.
Apparently
the bedding has been obliterated by weathering processes.
Good
bedding,
however, is
of the area where road
folds
(Figures 8,
found
cuts have
in the southeast corner
exposed cores of
9).
Two textural typos of bedded limestone
in sec. 29 T. 6 3., B
bution:
nites.
small
+
E.
and have
are exposed
a restricted distri-
Argillaceous calcisiltites and (2) BiocalcareBoth limestoxies exhibit medium bedding, + to 10
Cl)
inches thick.
1. Aril1aceous calcisiltite, On weathered sur-
faces these rocks have fine protruding laminae. The rock
contains calcite 1 to 20 microns in diameter, Calcareous
pellets 0.+ to 0.8 mm in
diameter are composed of erypto-
crystalline calcite.
2. Biocalcarenite, The bioclastic limestone has
wide, coarse laminae giving a graded appearance. The size
range of the calcite grains
is 36 to 62 microns.
Calcite
/
Figure 8
Dr&g fo1d exposed in road-cut normal to a lre
fold striking into photograph
Upper li!nestone unit
Martin Bridge formation
Location: StNW sec. 29, T. 6 S., R.
E.
Figure )
Close-up of fold from Fig. 7
artin Bridge formation
peilets (up to 20 microns) are coin
and are composed of
calcite microns in diameter (Plate 3, Figure 2).
Authigenic microcrystalline quartz replaces calcite
in scattered patches throughout the rock.
ny detrital
quartz and feldspar grains have been enibayed by the calcite.
Abundant narrow stripes of coliophane assumed to be of
organic origin, may represent the brachiopod Lin2ula.
Other fossil remains, alga]. structures and corals (6) have
been recrystallized into large single calcite crystals.
Limestone con2lomerate. Limestone conglomerate,
possible intraformational, is found near the
top of the
upper limestone unit and consists of limestone pebbles
in a veil-indurated matrix of silt and sand. Limestone
pebbles range from
to 30 mm in diameter, while other
rock types are smaller ( to 10 mm) in diameter
limestone pebbles are subround to subangular, whereas chart
and greenstone pebbles are rounded. The clast mixture is
veil sorted arid packed. (Plate
3,
Figure )+)
The limestone conglomerate is nearly 60 feet thick
and is found only southwest of East Eagle Mine. This conglomerate probably represents a restricted local deposl-
tional feature.
Greens tone conglomerate. Approximately 1,000 square
feet of a greenstone pebble to cobble conglomerate is present above the limestone conglomerate near the top of the
upper limestone unit in the southeast corner of the mapped
30
TABLE 9
COMPOSITION OF BEDDED LIMESTONES
Calcite
Quartz
Plagioclase
Potash feldspar
Magnetite
Clays
Collophane
Fossils
Corals
Bryo zoans
Algal structures
Limonite
Leucoxene
Microcrystalline quartz
Hematite
Calcite
31
TABLE 10
COMPOSITION OF LI)ST0NE CONGLORATE
Gzeenstone Material
Andesites
Limestone Types
Calcilutite
Calcisiltlte
Bioclastic
Calcarenite
Bas1ts
-albitized
ts ilic if led
"Vug" quartz
Chert
13
12
100% of
total limestone
boulders present
r.).)
IiJ
$!;IIt4M
Greenstone fragments
Chert
Quartz
Meta-quartz (8)
Plagioclase
Clays ?
Chlorite *
Epidote
Calcite
Authi 2enic Minerals
Microcrystalline quar tz*
Hematite
Calcite ?
*Chjef cementing agents
32
area.
Pebbles weathering out of the outcrop range from +
to 110 mm across their intermediate diameters.
The aver-
age roundness and sphericity for a number of pebbles are
.51 and .71+ respectively (23).
This conglomerate possibly
represents a local channel-till.
Thickness
The Martin Bridge formation apparently thins from
north to south across the thesis area.
Aerial photos were
used to estimate a thickness of 2,500 feet for the Martin
Bridge formation north of the northeast corner of the
mapped area.
On the southeastern side of Granite Cliff
in the thesis area, the marble has a calculated thickness
of 1,700 feet.
In upper Bradley Creek the minimum thick-
ness possibly including some tight folding is 1,1+00 feet.
Smith (31) measured a 630 toot section of Martin Bridge
southeast of the thesis area.
Au nd Fauna
Twenty-one fossil localities were found in the Martin
Bridge formation.
difficult.
Poor preservation made identitcation
Professor S. M. t4iller of Stanford University
identified the best material as follows:
33
TABLE U
COMPOSITION OF GREENSTONE CONGLOMERATE
Gre
tones
silioified
talbitized
Cbert
62%
2
20
Meta-sedinients:
13
3
Limestones-marbies
Argillites
i% of total
pebbles
examined
,)
Greenstone debris
Chart
Quartz
Feldspars (altered)
Chlorite*
Calcite
Calcite
Micro crys tafline quartz *
*Chjef cementing agents
Triass
Fl- 1. Crirxoid stem fragments, Cidaris spines
If.
same as #1
11. colonial coral - genera?
12. Cidaris spines
13. Pentacrinus stems
Cidaris spines
Terebratula sp.
16. Cidaris spines
17. Ralobia sp.
18. Halobia sp.
'nmonite - genera?
Triass (Zarnian)
19. Discotrobites sp., Ifalobia sp.
20. Halobia 89.
23. Halobia sp.
The Martin Bridge formation according to Mailer 's
identifications and listed ages, probably represents the
Karnian Stage of the Triassic System.
clastic material The source area for
the coarse clastic debris, excluding the limestone conglomerate, is the same source area which contributed to the
Lower Sedimentary Series. Minor fluctuations in the source
Pmvenance
area occurred throughout the deposition of the Martin
Bridge formation. Possibly one uplift in an adjoining area
occurred at the time the base of the laminated unit was
being deposited, resulting in the greenstone conglomeratic
limestone. The conglomerates indicate that some agent,
either waves or current action, was competent enough to
move the coarse debris into the carbonate environment.
The laminated calcareous siltatone represents a con-
dition of
continuous sedimentation in a restricted basin
3,
with subanaerobic conditions. Continuous sedimentation
is implied by the thick (580 feet) sequence of light and
dark rhythmicaliy laminated siltstone. The abundance of
pyrite and of restricted fossil forms suggests anaerobic
conditions. According to Petti3ohn (21+, p. 599) Linula
sp. which might account for the presence of collophane
and klalobia ap. are bottom dwellers that were capable of
living near anaerobic conditions. These bedded siltstones
also lack the bioclastic and coarse fragmental material
one would expect in a shallow near shore marine deposit.
The Upper Limestone Unit was deposited when bioherms
or reefs were built up to the wave base, The fragmental
and bioclastic nature suggests shallow marine deposition.
Increased wave action pn the local limestone sources
produced the limestone conglomerates. The restricted
greenstone conglomerate at the top of the upper limestone
possibly represents a small channel-fifl, or it may have
accumulated as the result of a submarine landslide of
greens tone material,
36
HUE WAL FORMATION
General Statement
Smith and Allen (30) used the name Hurwal for the
conformable series of argillaceous sediments capping many
of the ridges and peaks within the northern Wallowa Mountains.
The Ikirwal formation is named after the Hurwal
Divide which lies in the northeast corner of the Eagle Cap
quadrangle and the southeast corner of the Enterprise quadrangle.
The Hurwa]. formation covers approximately 11f square
miles extending across the southern and northeastern half
of the thesis area.
In the south central mapped area,
smooth rolling topography has developed on the Hurwal, but
where this formation has been dissected by streams, steep
talus-covered slopes occur.
The Hurwal characteristically
weathers along laminations and thin bedding planes, thus
giving a shaly appearance.
In this thesis the term Hurwal
is used for the thick sequence of dark argillaceous sediznentary rocks such as siltstonea and mudstones, including
lentils of massive limestone, limostone-greenatone conglomerate, and meta-sediments.
These rocks stratigraphi-
oally overlie the Martin Bridge formation.
The Hurwal
formation underlies the Columbia River basalt with steep
angular discordance,
Bridge formation.
but conformably overlies the Martin
37
The Hurwa]. formation is composed dominantly of argil-
laceous rocks with varying degrees of induration and metamorphism.
No single area exists where a contact could be
placed to separate "argilhites" from other siltstones or
muds tones
The northern and western limits of the Hurwal were
metamorphosed to various degrees during the emplacement of
the WaUowa batholith.
In the northeast corner of the
mapped area, the rocks are micaceous and less carbonaceous.
from Lime Creek southward, the rocks maintain a dense,
black, fine-grained carbonaceous character and appear to
be slaty (Figure 10).
These rocks will be discussed wider
the ?4eta-sediment subheading of the Hurwal formation.
Petrograv.
The siltstones, mudstones and argil-
hites are of two variOties:
(1) laminated siltstones
(Figure 11) and (2) bedded siltstones.
dividual laminae are variable.
Widths of the in-
From a few laminae meas-
ured, the coarser laminae averaged +.2 mm thick compared
to l.1f mm for the fine dark, carbonaceous lninlnae (Plate
6, Figures 1, 2).
Bedded siltatones commonly occur in
thin and medium beds 1 to 8 inches thick.
Many of the laminations exhibit micro-flow, load
casts, and fine scale cross-bedding, suggesting current
direction, sediment movement or sedimentation direction.
-'ui:
4
4
-
d
,-
S
-,.
L;
FIgure 10
Norir dcte, carbonoceous argillite
Hururl formation
Location; S* sec. 1?, T, 6 8., R. +1+ E.
FIgure 11
Laminated slltntonec and mudstones on Dixie
Creek
Iiurtai forriictIon
Location:
F* sec. 35, T. 6 3., R. 1+3 E.
Micro-faults are numerous in siltstones from upper O'Brien
Creek (Plate 6, Figure 3).
The light-colored, coarser laminae are generally
more calcareous than the tine, dark, thin-bedded siltetones.
Pyrite is common to all the siltstones, but is more predominant in the dark carbonaceous types.
Fragments of
fossils, limestone pebbles and volcanic rocks are commonly
found in the carbonaceous siltetones.
Massive, white to gray limestone occurs in the
o 'Brien-Bradley Creek area and along upper Jack Creek and
Gold King Creek.
Some limes tones which were mapped as
Hurval in Bradley Creek and Gold King Creek may be Martin
Bridge interfolded with the Hurwal.
PetroraJiv.
The northern lentils have been
re-
crystallized more extensively than the southern lentils.
Large "sparry" calcite veins commonly extend throughout the
rocks.
Stylolites are abundant separating the many tex-
tural varieties of limestone.
Calcite grains range in size from
to 70 microns,
having the elongated grains somewhat aligned.
Pellets (26
to 90 microns) are composed of calcite 3 to 7 microns in
size.
The length to width ratio at the pellets is near 2:1
(Plate +, Figure 1).
COMPOSITION OF SILTSTONES AND ?IJDSTONES
Quartz (8)
Leucoxene
Igneous
Chart
Sericite
Chlorite
Biotite
Metamorphic
Limonite
Andseizie
Calcite
Magneti te
Ilmenite
Clays ?
sp.
7lalobia
Hematite
Ammonite fragments
Mi crocrystaUine quartz
Calcite
Carbonaceous matter
Pyrite
TABLE 3.3
COMPOSITION OF TIlE LOWER LIMESTONE LENTILS
Detrital Material
Calcite, fragmental
Vdcanics, (greenstones)
Hematite
Clays?
rwi
Sheil fragments
Algal structures
Crinoid stem fragments
Echinoid spines
Worm tubes ?
Carbonaceous matter
Alterationlreervs talli zed
Minerals
Phiogopite
Limonite (minor)
Microcrystalline quartz
Calcite
I
Conglomerates are scattered between Skookum Creek
and O'rien Creek as lentils 60 to 200 feet thick without
apparent stratigraphic regularity.
Outcrops of the con-
glomerates have more pronounced reliet than adjacent siltstones, and generally do not exhibit signs of bedding
(igures l2
13, 11i).
Petioraphr.
The coarse elastic debris range from
granules to cobbles with a few boulders.
Some conglomerate
lentils are primarily composed of granule size material.
Poor sorting and packing is evident in the coarse conglom-'
erates, but this is not the case in the granule conglomerates.
Roundness and sphericity measurements of one con-
glomerate set were .6 and .72 respectively.
The matrix material varies.
One conglomerate may
be cemented by silt, clay, and siliceous minerals while
another matrix consists of calcite, silt, and alteration
minerals.
Granule conglomerates are tightly packed, well sorted
and extremely well indurated by siliceous and recrystallized
minerals.
UDDer Lime atone Lentils
The upper limestone lentil area is situated along
East Goose Creek and Eagle Creek in the southwestern part
of the thesis area.
Limestone crops out in sections 28,
Fiçure 12
Sote pobblos uortiier1n i'rom poorly inrtoi
con1oiuerto
Greentono conC1onerate lentil
flurwi1 form,t ion
Locction: NE* sec. 25, T. 6 8., R. 3 E.
13
Clo$o-up of pobb1o; in Fig. 10
Note the degree of phericity and roundnoc
Hurwnl $orriatio
)i3
.
Lju..0
c11 indurated conglonierate
Linetone cobblen weather out of the outcrop
Liinetone-)reer1stone co1ouerctto lentil
Hurwnl forniation
Location:
Ets1k, sec. 2o, T. 6 3., fl. 1.3 E.
Finure l
Contorted recrtallized liniotone
Recr"tal1izt1on has not obliterated foil rem'in
Lliuestorte 1eitil
Hur'jt'1 formation
Location:
t*N
sec. 2G, T. (
,
1.3 L.
TABLE :i)+
HURWAL FORMATION
!) T)
Limestone
Bioclastic
Rare
Cal carenites
Volcanics (greenstones)
Very abundant
Ba salts
ii Ic ir led
Andesites
Chart
Argilhite/mudstone
Common
Common
Common
QLlar tz
;c
.)
f
Quartz (8)
Metamorphic
Chlorite*
Igneous
Plagioclase, altered
Chert
Limes tone
Greens tones
Sericite
Epidota
Biotite
Limonite
Leucoxene
Ba salts
Andasites
Clays ?
Feldspar s
Carbonaceous
matter
Hematite*
Microcrystalline
Pyri te
Calcite *
Cexsenting agents
quartz*
S
33 and 31f, T. 6 5., R. )+3 E. and may correlate with the
limestones in section 27, T. 6 S, R. F3 E. and sections
26 and 35 T. 6 S., R. +f E. (Figure 15).
st ol the len-
tils are 50 to 150 feet thick.
?etroRrathr.
The massive white to gray limestone is
composed of well-packed and sorted, angular to subangular
fragmental limestone arid fossiliferous debris (flate 5,
Figure 1).
Limestone fragments of 1 to 3 mm in diameter
are common.
A few extend to 30 mm.
separated by stylolites.
Some fragments are
Individual calcite grains from
8 to 90 microns in size comprise most fragments.
Calcite
grains in thø matrix are 10 to 180 microns in size.
Pellets
(1i5 by 180 microns) are composed of calcite 2 to 8 microns
in size (Plate 5, Figure 2).
The limestones range from
biocalcarenites to calcarenites.
Recrystallization and replacement of calcite by
microcrystalline quartz has taken place in most rocks.
Lu
Fauna
Twenty-seven fossil localities were sampled in the
Hurval formation within the thesis area.
Preservation of
the fossils is better than in the Martin Bridge formation.
The best material was identified arid dated by Professor
S
W. )il1er as follows z
TABLE 15
COMPOSITION OF UPPER LIMESTONE LENTILS
Detrital Material
Volcanics (greenstones)
Basalts
Calcite
Quartz
Plagioclase, altered
Clays?
Magnetite
Alteration/recrystallized
Minerals
Leucoxene
Limoni te
brpr
Carbonaceous matter
Fossils;
Echinoid spines
"Pellets"
Algal structures
Worm tubes?
Bryazoans
Shell fragments
Algal dust (1,1)
Hematite
Crypto crystalline quartz
if 7
Upper Triassic
Fl-27 Halobia sp.
28
Aiamonite, genera?
29 Ealobia sp.
30
ra1okj
sp.
30b iacotrotites sp.
Karpian
31
a1o.a cf. rugosa
Halobia cf. rugosa
33 lIajobia cf. rugosa
Triassie
37 lialobia sp.
3
TJppe
Uper Tria.jurassic
370
tzu
38 Crinoid
Cidaris
)Lf
Halobia
sp. (colonial coral)
stem fragments
spines
sp.
1,6
Haloj
if7
if8
HalobIà ep.
Halobia or Daonellafl
ap.
0 Ualobia ep.
51#
Isastrea ap.
Many indeterminable ammonites, pelecypods and shell
fragments were among the fossiliferous
The colonial coral
according to
debris.
ep. (Fl 37° and Fl 5sf)
iUer, can be either Jurassic or Upper Tn-
assic in age, but is more likely Upper Tniassic,
The
Martin Bridge is considered as Karnian; therefore, the
Hurwal being a rather thick formation, may extend from
ICannian into Nonian.
According to Smith and Allen (30, p.
11,) the Hurwal is uppermost Karnian and Nonian.
Thiekneas
The top of the Rurwa]. formation is not exposed, so
the total thickness cannot be accurately determined, A
paced traverse south of Bennet Creek to West Eagle Creek
using Mandelbaum and Sanford's (18) method for
computing
a stratigraphic section gave a minizmam thickness of #,l00
feet for the Hurwal formation.
Northwest of Granite Cliff
to the contact of the batholith, the Hurwal is estimated
from the map to be 6,800 feet thick.
As stated previously the Hurwal formation conformably
overlies the Martin Bridge formation.
The relatively flat
lying basalt overlies the steeply dipping Hurwal.
There-
fore, the Columbia River basalts overlie the Hurwal with
angular discordance
Provenance
Environment
Deposition
The source area which contributed elastic material
to the Lower Sedimentary Series and the Martn Bridge formation is the same source area that contributed to the Eurwa].
formation. Altered volcanic debris present in the Lower
Sedimentary Series and Martin Bridge formation is similar
to that found in the Hurwal formation.
The southwest corner of the thesis area is regarded
as the uppermost exposed part of the Hurwal formation.
Here, the formation contains greenstone granules and pebbks
within the limestones.
Conglomerates in the south-central
portion of the mapped area are also composed of greens tone
material.
This material was transported and deposited
quickly as indicated by poor sorting, packing, and mixture
of immature rock and mineral assemblages.
The various source areas presumably were reduced to
a lower relief at the beginning of the &u'wal.
Possible
1F9
humid climatic conditions initiated vast chemical weathering
on the volcanic source areas which in turn permitted the
removal of a voluminous amount of argillaceous material.
The fine-grained laminations and bedded argillaceous
rocks represent a long cycle of continuous deposition in
deep, restricted water with
bic conditions.
alternating anaerobic and aero-
The laminations may have been formed by
affecting the rate of
different sized particles (28, p.
some type of cyclic sedimentation,
supply or deposition of
According to Rubey, (28) preservation of laminae
suggests quiet water,
indicating that they accunnilated
below depths in which wave action existed.
The presence of well-preserved laminations also suggests the absence of benthonic scavengers and may indicate
anaerobic bottom conditions.
Anaerobic
conditions are
also denoted by the abundance of pyrite and organic matter
found in the siltatones.
Every siltstone sample which was
broken down by a sodium oxalate solution contained numerous
authigenic cubes of pyrite; and commonly, a sewn of carbon
ringed the containers.
Isolated limestone lentils suggest a
possible shaflowing of the seas.
warming arid
Most of the limestone
lentils are composed of fragmental and bioclastic
limestone
debris which probably accumulated from the eroded detritus
of reefs or bioherms.
Also, the general absence of pyrite
in the limestones suggests that aereated conditions existed.
Two localities of colonial coral Isastrea ap. (F]. 37c
and F]. 5) indicate coral growth in the area during the
upper Triassic.
According to Vaughan (36) madreporian
corals began a vast growth expansion during the Upper Tnassic and reached an area]. extent as far north as 600 north
latitude.
conditions:
Colonial corals can thrive only wider certain
relatively shallow, warm, clear, circulating
marine water in which sedimentation is very slow or completely lacking (36, p. 68).
META 8DIMENTS
General 8tatement
The Hurwal formation has been intensely metamorphosed
near the contact of the Wailowa batholith. According to
Krauskopf (10, p. 619-621), the most intense zone of metamorphism nesi' the entire batholith is on Thimmtngbird l4ountam in the northern part of the thesis area where many
metamorphosed rocks of the Hurwal formation are strongly
foliated within a few hundred feet of the quartz diorite.
Farther from the
contact of the batholith, as in the area
between upper Dixie Creek and the Forks Forest Camp, the
metamorphic rocks are mostly argillites which contain a
few patches of
marble and contorted limestone.
For simplicity, the metamorphic rocks will be discussed by areas.
Many rocks along the quartz dioritic-Hurwal contact
on Hummingbird }buntain are gneissio and grade away from
the contact within a few hundred feet into a schistose
texture.
Several thousand feet from the batholith on the
southeast slope of Thmm1gbird )untain, the rocks retain
a schistose appearance although the original sedimentary
laminations and structures remain intact.
A few rocks ap-
pear hornfelsic, and some rocks near the contact, have
slight hypidomorphic-granular texttires similar to that of
the quartz diorite.
Z4a3or constituents as seen in.
six thin sections are
hornblende, and biotite. Potash feldspar
and diopside are minor Other minerals identified are
aridesine, quartz,
spherte, apatite, zircon, iron ore, epidote, aila.nite, and
pyr'ite.
In the strongly foliated rocks, grains of hornblende
and biotite are generally aligned within the dark bands,
whereas granoblastic quartz and andesine form the light
colored bands.
Forks Forest Canrn-UDper Dixie Creek
rble. Small outcrops of saccharoidal marble in
upper Dixie Creek (NW* sec. 23., T. 6 8., R. f3 L) con-
sist essentially of granoblastic calcite. Occasionally,
the calcite is replaced by microcrystalline quartz (Plate
t1, Figures 3
and )+)
Interstitial phologopite is also
abundant.
Other recrystallized limestones found in the NE* and
NW* sec. 28, T. 6 S., R. f8 L, exhibit thin, light and
dark color banding due to alternations of carbonaceous
material. }bst of the outcrops of limestone are contorted
(Figure 15). Recrystallization of the limestones has not
obliterated fossil remains, and only in places are rocks
partially granoblastie.
Argillites. Areas of firte-grained metamorphosed
siltstones (SW sec. 22, SW sec. 21, and NW4 sec. 28, T.
6 8., B. )+3 E.) are commonly blastopelitic. The lightcolored bands are composed mostly of granoblastic quartz,
whereas the dark bands are composed of dark minerals which
are too fine for accurate identification (Plate 6, Figure
1g.),
One dark mineral is apparently diopside.
Many of the bands are contorted and possibly repre-
sent minute drag folds.
Many stretched pebbles of limestone
are found in the argiilites.
The argillaceous sediments
in the Forks Forest Camp area were primarily metamorphosed
by the intrusion of the inelagabbro.
COLUMBIA RIVER BASALT
Gnera1 Btatemen
I. C. Russell (29, p. 132) first applied the term
"columbia lava" to widespread Tertiary basalts of central
Washington in 1893. Merriam (19, p. 303) restricted the
term "Columbia lava8" to thick sections of Mtocene basalt
along the Columbia River. These rocks are generally known
as the Columbia River basalts. Ross (27) and Smith and
Allen (30) assumed that the basalt in the southern Wallows
)buntainn to
basalt.
plateau in the north central
be Columbia River
The top of the basalt
area is
gently
rolling topography. Where the edges of the flows are ex
posed by stream dissection, mainly in the western part of
part of the thesis
relatively smooth with
the area, slopes are steep and covered with talus (Figure
16).
area range
from basalt to olivine basalt flows and dikes. ?bst weaThe Columbia River basalt in the thesis
thered outcrops are red to rusty-red, with fresh exposures
being black to dark greenish-black. Red soils are characteristically developed
rounded to
on the
Columbia River basalt with
subrounded boulders remaining in and on the soil.
The upper few feet of individual flows are often very
vesicular.
Figure 16
Edge of a basalt floLj
Note thickness and poor columnal jointing
Columbia iliver basalt
+ E.
Location: SE* sec. 18, T. 6 3., R.
Figure 1?
Note long linoc.r trends of basalt feodor dikos into
batio1ith
Columbia River basalt
Location: Tuo miles north of upper West Eagle Creok
56
Throughout the thesis area, textures and mineral corn-
positions of the basalt flows vary both laterally and vertically.
Some basalt flows are porphyritic while flows
200 feet below are totally aphariltic.
basalt feeder dikes are aphanitic.
Nearly all of the
A greater abundance of
pigeonite over augite was noted between two vertically
separated flows in the east-central thesis area.
Pri'ry constituents of the Columbia River basalt
are labradcrite, augite, pigeonite, and olivine.
Magnetite
is a constant accessory mineral, and most thin sections
contain gray to brown glass.
Labradorite forms large phenocrysts in the porphyritic
basalts and small laths in the subophitic and glomeroporphyritic basalts (Plate 7, Figures 1, 2).
Labradorite,
commonly containing oscillatory zoned cores, exhibits albite and albite-carlsbad twinning.
Pyroxene is represented by both augite arid pigeonite.
Augite occurs as phenoeryste which are sometimes poikilitic, and also as granules in the groundaass.
Pigeonite is
less common and likewise occurs as phenocrysts and as grantiles in the grouridmass.
Olivine generally occurs as small anhedral pbenocrysts.
However, in the porphyrltic basalts, olivine forms large
euhedral grains.
57
Magnetite is fine-grained, commonly euhedral, and
exists both in the groundmass and as inclusions in labradorite. As much as 20 per cent of magnetite is present
in one thin section (Table 16).
Gray to brown, isotropic glass is present in most
thin sections. In some thin sections brown glass contains
abundant labradorite microlites.
Alteration products are abundant. An alteration
product, possibly chlorophaeite, similar to palagonite
but more birefrigent is abundant in thin sections (22).
Linionite altering from opaque minerals is common. Iddingsite or red iron oxide rims are common around olivine.
Structure.
Vertical columnar jointing is veil developed along
upper Gold King Creek and on the east side of Bennet Peak.
Horizontal plates two to four inches thick are developed
in the basalt in upper Dixie Creek (s sec. 23, T, 6 3.,
3 E.).
fftratigaiic Relations
R.
Columbia River basalt in the thesis area unconformably overlies about 20 square miles of Upper Triassic sediments and Lower Cretaceous batholithic rocks.
A distinct angular unconformity exists between the
steeply dipping Triassic sediments (+O to 800) and the overlying, relatively horizontal Columbia River basalt.
COMPOSITION OF COLUMBIA RIVER BASALT
Labradorite
Pyroxene
Olivine
Magnetite
25
3
31
20
35
20
6
20
36
2+
23
9
100%
100%
50
20
2
11
Glass plus
alteration
products
Total
66
22
3
5
100%
100%
-
100%
Modes or tour typical Columbia River basalt samples
and one basalt feeder dike sample.
*salt dike
Explanation:
G-l6
0-17:
G-l69
NE*, SEL, NEk sec. 1?, T. 6 5, R. +f E.
SW, NE*
sec. 17, T. 6 S., B. 4k
NE+ sec. 8, T. 6 8., R. f3 B.
0-173: $E* sec. 6, T. 6 8., R.
3 B.
0-231: Center of Sec. 10, T. 6 8., B. #3 B.
59
Thicknes
The total number of flows present in the area is not
biown.
On the east side of Bonnet Peak approximately eight
flows can be distinguished and at least twenty flows occur
in the drainage of West Eagle Creek.
Thickness of individual flows generally varies from
10 to 60 feet; however, one of the thicker flows at the
head of Gold Xing Creek is nearly 100 feet thick,
The flow
below it, concealed by talus, may be as thick as 200 feet
(Figure 16).
The thickest section of Columbia River basalt is on
the east side of West Eagle Creek in the western portion
of the area.
Here the basalt attains a mar1mwn thickness
of 2,100 feet.
No exact age can be given the basalt from data collected in the thesis area.
However, basalt flows cap many
peaks in the Cretaceous batholith and numerous basalt dikes
extend throughout the batholith; moreover,
ch of the
glacial material in the thesis area is composed of basaltt
debris.
Therefore, the age of the Columbia River basalt
ranges between Early Cretaceous (4Albian) and pre-Pleistocex.
Elsewhere in Oregon, a Middle Mioceno age is well established for the columbia River basalt (i, p. 83).
The Columbia River basalt poured out in the thesis
area through a series of fissures which cut through the fri-
assic sediments and the granitic rocks of the batholith.
Most feeder dikes in the Wallowa Mountains have a northerly
trend.
In the batholith the rust-red outcrops of the dikes
are easily traced against the thite background of the
granitic rocks.
Most basalt feeder dikes range from 5 to
+O feet in width and have long linear trends (Figure 17).
QUATERNARY DEPOSITS
Glacial deposits in the mapped area consist of sub-
round to round boulders of quartz diorite, basalt and
morphic rocks in a fine-grained, structureless, buffcolored matrix.
All the glacial deposits in the thesis
moraines.
tures are discussed under Geomorphology.
area occur in lateral and terminal
Glaeio-fluvj,al gravels.
extend
along
meta-
These fea-
Gravels mapped with alluvium,
Eagle Creek from the Forks Forest Camp to the
confluence of Dixie Creek.
100 feet above Eagle Creek.
Some gravels are as much as
Round to well round cobbles
of various compositions are found poorly
stratified in a
fine brown matrix.
sorted arid un-
These gravels are pos-
sibly the product of glacial melt-water transportation.
Alluvial Deiosits
Alluvium consists of reworked glacial debris and
eroded material that has accumulated as alluvial fans or
valley fillings during spring runoffs.
Landslide
slump deposits. A few landslide or
slump deposits are present in the thesis area.
The largest
area is found west
of the
East Eagle Creek.
This mass apparently slid-off of the dip
slope of the }hu'wal
confluence
formation.
of Hudson Creek with
62
Another such area is located on the south side of
lower O'Brien Creek where a mass Columbia River basalt apparently has slid-off of the side of the ridgø.
The glacial deposits can be referred to the Pleistocene, and the younger deposits which comprise fans and
valley fillings are of recent age (2?, p. 60).
63
INTRUSIVE UNITS
QUARTZ DIORITE
Granitoid rocks of the Wallowa batholith extend
southward into the northern part of the thesis area where
the rock has the composition of a quartz diorite.
Quartz diorite covers about three square miles in
the north-central part of the thesis area.
Most of this
quartz diorite is on the uplifted side of a large normal
fault which forms the southern boundary of the Wallowa
Post-Middle Miocene uplift of this fault block
Mountains.
enabled Pleistocene glaciers to produce the alpine topography which typifies most exposures of quartz diorite.
Petro2raphY
Modal analysis of ti've specimens of granitoid rock
from the batholith are given in Table 17.
Four analyses have
the composition of a quartz diorite arid one mialysis has the
composition of a granodiorite.
However, as only one thin
section was prepared from each rock, ax
as most thin sections
are small, individual modal analyses are not definitive.
Nevertheless, the average composition of the five analyses
should give a close approximation of tha actual p ercentages
of major minerals in the quartz diox'ite of the thesis area.
Major constituents of the quartz diorite are andesine
(An 38 to An.
biotite.
6), alkali feldspar, quartz, hornblende, and
Accessory minerals are apatite, zircon, monazite,
sphene, allanite, and ore minerals.
Thin sections of the quartz diorite exhibit hypidomorphic-grinnlar textures which commonly are modified by
cataclasis.
Grain sizes range from oa to four
Large myrmekitic
mm
in
.amet'.
intergrowths of wormy quartz and andasine
are veil developed in some thin sections
(Hate 7, 1.guie
3).
Quartz commonly displays pronounced wavy extinction ELate 7,
Figure 1) arid some quartz recrystailized during deformation
into a msaic of
ardar grains. Wiere recrysta1llRtion d quartz
has occured bkvttta generally exhibits intense bending, and
plagloclase shows less extreme beictthg of twinning laniel].ae.
Albite
and Albite-Carabad twinning are commonplace.
Oscillatory zoning prevails throughout the interior of the
crystals which are rimmed by normal progressive zoning.
Green hornblende and brownish biotite are the mafic
minerals
Zircon and apatite inclusions are commonly
found
in the biotite.
Biotite is commonly altered to chlorite and granular
stringers of aphene.
Although some epidote accompanies
the chloritic alteration of biotite, epidote also occurs
as an alteration of plagioclase and hornblende (35).
Some
plagi.oclase is mildly altered to white mica.
According to Taubeneck, (33, p. 1685) the eastern
Oregon plutons have strongly deformed Upper Triassic and
Jurassic (Cailovian) rocks; whereas Cretaceous rocks in
65
TABLE 17
COMPOSITION OF QUARTZ DIORITE
Sample No.
Potash feldspar
Quartz
Plagioclase
Biotite
Hornblendo
Apatite
Chlorite
Epidote
Sphena
Ai.anite
Zircon
Iron Ore
Total
G-i8
3.3
21.3
56.0
11.6
7.3
0.1
0.1
T
T
T
0.0
0.].
100%
G-160
G-16c
3t,.,2
19.0
2O.
63.7
61.5
6.5
1,8.o
2.
90
9.'+
0.1
1.0
0.0
0.3
0.0
T
0.6
100%
T
0.3
0.0
0.2
0.0
0.0
0.0
100%
G-27
8.7
9.7
10.9
0.2
0.5
T
T
0.0
0.0
0.2
100%
Modes of five gi'anitoid rocks from batholith.
6.8
19.8
51.5
12,33
8.9
0.0
0.2
0.1
0.0
0.1
02
0.1
100%
is closest to a granodiorite. The remaining four are 0-158
quartz diorites.
Explanation;
0-158
SWSE*E*sec,6T,6S.,R.fE.
0-160 NWéSW*sec.6T.6S.,R.+'fE.
0-165
SW* sec. 6 T. 6 S., R. 1+f E.
G-27+ NW*sec.1T.6S.,R.+3E.
0-275 One-fourth mile SW of G_27+.
eastern Oregon are relatively undeformed. In central Oregon,
tonalite and granodiorite pebbles occur in marine Cretaoeous
conglomerate of Albian age, Such evidence indicates that
the granitic plutons are post-Callovian and pz'e-Albian.
A small intrusive of melagabbro, exposed over an
area of approximately three-fourths of a square mile, is
located one mile north of the confluence of Eagle Creek and
West Eagle Creek. Although its content of plagioclase
varies considerably, most thin sections contain about +0
per cent calcic plagioclase (An 8 to An 60) (9), and O
per cent altered clinopyroxene; therefore, most of the intrusive is a melagabbro.
The hard, dark-green outcrop on the west side of
Eagle Creek is nearly confined by glacial material. Stream
erosion has uncovered the western and small eastern outcrops. Even though the rocks are fairly resistant to
weathering, they do not have pronounced relief.
The main constituents of the original rock were augite, hypersthene, and calcic plagioclase. Minor quantities of brown hornblende rim augite which contains a few
relicts of olivine.
roxene to
talc and
Metamorphism altered much of the pyfibrous amphibole.
Slender needles of
actinolite penetrate plagioclase and occur as isolated
clusters within the plagioclase, Accessory minerals are
iron ore and apatite.
6?
GEORPI1OLOGY
)bst geomorphic features in the thesis area are the
result of Pliocene block faulting and Pleistocene glaciation.
Alpine glaciers dissected the northern part of the
mapped area and spread glacial debris southward along the
major streams. Features characteristic of alpine glacia-
tion ares
Glacial valleys
AU three major stream valleys extending into the mapped area from the north were modified
by glacial action. West Eagle Creek, Eagle Creek and East
Eagle Creek exhibit the characteristic U-shape of glaciated
valleys (Figure 19).
Many small valleys and gullies on the
east slope of Thiminlngbird Iuntain have been furrowed by
glacial action.
Ciraue lakes.
Looking Glass Lake and the smaillake
heading the middle fork of Hudson Creek occupy cirque
basins. Glacial strale and polish are present on the
granitic rocks along the outlet of Looking Glass Lake.
The depression west of Looking Glass Lake, and the
depression in the upper north fork of Hudson Creek are two
small cirque basins
Both basins are symmetrical and steep-
sided with a rather high beadwall.
68
Figure 18
5na11 well developed 1cterc.]. moraine at
the base of llurnmfngbird
untain
Location: North central thesis area
Figure 19
East Icgle Valley
Jote the characteristic U-shape of a
glaciated valley
Artes
g i',orns..
Hwnmingbird Mountain represents
a poorly developed serrate ridge.
Better developed arates
can be observed farther to the north outside the thesis
area,
One small under-developed horn can be seen on the
ridge southeast of Looking Glass Lake.
Of the three cirques
surrounding the horn, headward erosion on the northern side
was never completed for the development of a classic born.
Moraizi.
Lateral morainos parallel the three major
streams in the thesis area.
The largest and longest lat-
oral moraine parallels Eagle Creek, and debris is found
1,000 feet above the stream on the east canyon wall.
From
the vicinity of Boulder Park Resort the moraine tapers
southward for about four miles.
Morainal material in the
vicinity of the Forks Forest Camp may possibly represent
a terminal moraine from the Eagle Creek glacier.
Lateral moraines along East Eagle Creek are best exposed on the western slope for about one mile north of
Gold Xing Crek.
the valley floor
Morainal debris is found 800 feet above
ich of the moraine has been removed by
recent erosion so only small patches are 1eft
Jack Creek
marks the southern limit of this moraine.
Morainal debris along West Eagle Creek also extends
about 800 feet above the stream,
This moraine ends in a
terminal moraine at the confluence of Grove Creek and West
Eagle Creek.
The small spur north of Two Color Lake is considered
a lateral moraine marking the eastward turning of a small
glacier (Figure 18). The spur is well-shaped, symmetrical,
and is an extension of the wall of metamorphic rocks to
the northwest. Glacial debris east of the lake possibly
represents the remnants of a terminal moraine. The un-
sorted, unstratified debris consists of angular to subrounded metamorphic rocks in a fine brown interstitial
matrix.
"teneei"
Rounded granitic
boulders and gabbroic oob-
blea occur in the SEe NW* sec. 22 T. 6 S., B. +k E.
Gra-
nitic boulders were not found at the 6OO foot contour in
the northern part of sec. 22 where the gabbroic intrusive
is located. It is assumed therefore that a "veneer" of
glacial material extended across all of section 22 during
some stage of Pleistocene glaciation. Except for a few
remaining granitic boulders, most of the veneer was removed by post-Pleistocene erosion.
Alluvial fans.
Two well developed alluvial fans
covering approximately one-half square mile coalesce at
the mouths of Hudson
Creek and Little Kettle Creek.
Both
fans are composed of subangular to round, poorly sorted,
unstratified cobbles and boulders of various rock types
with large amounts of fine interstitial material.
Fans
7].
are also well developed along Eagle Creek, but are much
smaller than those along East Eagle Creek.
All alluvial fans were formed by vigorous erosion of
the adjacent highlands, and were deposited principally by
spring runoffs.
Presumably during the Pliocene, the northern part of
the thesis area was uplifted by normal faulting.
Faulting
occurred after the extrusion of Columbia River basalt and
prior to Pleistocene glaciation.
Airing the Pleistocene, alpine glaciation modified
most existing topographic features.
Debris derived by
recent erosion of the highlands has filled in valley floors
and built alluvia], fans
Overall erosion has had little
effect on modifying the topography created during the
Pleistocene.
72
STRUCTURAL GEOLOGY
The major structures in the thesis area consist of
folds, faults, and intrusions of' quartz diorite and gabbro
(See
63).
'.
Mfl
A large overturned anticline which strikes northnortheast and overturned to the northwest, extends along
the eastern edge of the mapped area.
Overturning is indi-
miles to the east on Red ibuntain by Wethereil (37,
p. 196) and by the stratigraphy of' the thesis area. In
the northeast corner of the area, attitudes of' the overcated 5
turned strata range from 70 to 900 trending to the southeast.
In the east-central portion of the mapped area, the
attitudes still maintain a southeastern dip of 60 to 82°.
A secondary fold system normal to the overturned
anticline is centered about
the East Eagle Mine.
This
cross-fold represents a small northwest-plunging, tightly
folded anticline overturned to the northeast along the
northern limb. Attitudes along the northern limb are overturned 65 to 75°. Both limbs of the anticline are composed
of tightly-compressed near-isoclina]. and fan folds.
The
small digital-shaped outcroppings of the Upper Limesne
Unit mapped south
of the East Eagle Mine, may represent the
cu1nination of individual isoclinal folds.
73
The northern limb of a northwestern plunging syncline
nearly parallels Eagle Creek along the southern thesis
boundary. The remainder of tim structure lies to the south
in the Sparta quadrangle (26). This syriclinal structure is
well situated geometrically in relation to the northwest
plunging anticline which lies to the northeast.
Northeast trending cross-folds and cross-faults
normal to the synclina]. axis are numerous in the Sparta
quadrangle (26) and may extend into the thesis area.
The emplacement of the batholith has possibly affected
attitudes in the northern and northeastern area by rearranging the strike of the lithologic units subparallel to the
outline of the batholith. This may account for the circular
arrangement of the attitudes within a three mile radius of
the batholith.
Folds
Because of the foliated rocks and the
rearrangement
of the strike in the Hurwal formation near the batholith,
folding imast have taken place after the deposition of the
Hurwal formation (Karnian-Norian) and prior to the intrusion of the batholith (post-Cailovian - pre-Albian).
Folds were not observed in the basalt; therefore, it
is assumed that no major folding has occurred
in the thesis
area since the extrusion of the Columbia River basalt (postMiddle Nb cone).
Faults
A small wrench fault extends along the course of Gold
King Creek.
Criterion for strike-slip movement along this
fault is a large drag fold formed in the Martin Bridge Up.per Limestone Unit SE* sec. 17, T. 6 S., R. +1f E.
Attitudes
on this fold trend to the southeast except when approaching
the fault.
Near the fault the strike of the attitudes curve
until they strike to the northwest.
A strike-slip component
of 500 feet is estimated from the map.
A second fault possibly related to the cross-folded
structure and normal to the major overturned anticline,
parallels the northern side of Jack Creek.
No displacement
of the Columbia River basalt was observed.
A possible third fault may exist on Lime Creek thancating the Martin Bridge formation.
The limestone fails to
crop out in the creek in its proper position.
A fourth fault is suspected parallel to Bradley Creek.
The single criterion for a fault is the abrupt termination
of the limestone lentils in lower Bradley Creek.
Prostka
(26) also extends a cross-fault parallel to Bradley Creek,
up-throwing the western block.
The fifth and largest fault in the thesis area extending five miles west-northwest through the northern area,
uplifted crystalline basement rocks and associated Triassic
metasedirnents on the north from the plateau-capping basalts
and Triassic sediments on the south,
The vertical
displacement of the fault as estimated from data in the
thesis area is at least l,OO feet.
A sixth fault extends four miles across the southern
halt of the mapped area.
the north.
This fault is also uptbrown to
The trace of the fault can be followed by sznsll
patches of basalt remaining on the ridges in the southcentral area.
Faults
The Gold
ixig Creek and Jack Creek faults have not
noticeably displaced the Columbia River basalt, yet both
long northwest trending faults have displaced the basalt.
Presumably, two cycles of faulting has occurred in the
thesis area; postNorian
Miocene - pre-Pleistocene.
pro-Albian and post-Middle
76
HISTORICAL GEOLOGY
Airing the Permian and Triassic periods an eugeosyndine (7, p. 33-1f0) existed along the western margin of
the North American continent.
Throughout northeastern
Oregon, the Permian was characterized by extensive vulcanism.
By the end of the Permian the eugeosyncline had
nearly filled with volcanics and interfingering terrestrial
sediments (39).
The present area of the southeastern
Wallowa )buntains then subsided and filled with intercalelated pillow lavas and sediments which in turn were cov-
ered by a thick marine sedimentary sequence (39, p. 2O3-2O).
Lower and Middle Triassic rocks are not found in the
thesis area.
Also, very little is known about the Lover
and Middle Triassic rocks of northeastern Oregon.
Earlier
workers such as Ross (27), Smith and Allen (30), and Gilluly (Ii) assumed a period of erosion during this time.
However, recent data by Prostka (26) and Wetherell (37)
indicate a
conformable and in part a gradational sequence
frOm the Permian into the Upper Triassic.
Airing the early Upper Triassic, orogenic movements
uplifted
volcanic rocks such as the Clover
Creek greenstones
and simultaneously depressed adjacent eugeosynclinal areas.
Vigorous erosion of an uplifted greenstone area and possibly
a hypothetical volcanic archipelago produced the coarse
detritus
of the volcanic conglomerate
of the Lower
77
Sedimentary Series,
The local greenstone source area and
other source areas containing sedimentary, granitic, and
metamorphic rocks wore subseajiently reduced.
Fine clastic
material accrnilated, but sporadically, coarser sediments
were deposited.
After deposition of the Lover Sedimentary Series,
the volcanic areas were partially reduced, and the eugeosynclinal trough nearly filled.
Shallow depths, possible
warming of the seas, and abundance of organisms initiated
carbonate sedimentation.
Limestone was deposited con-
tinuously until the middle-late Kárnian when carbonate
deposition ceased in favor of argillaceous sedimentation.
chemical weathering was severe on the slightly elevated volcanic source areas.
A voluminous amount of ar-
gillaceous material was deposited from the middle-late
iCarnian into the Norian.
Apparently local shallow areas occurred intermittently
in the thesis area during the argillaceous sedimentation,
thus enabling the growth of small reefs or bioherms.
&st
of these structures were subsecpiently destroyed by wave
and current action and redeposited as fragmental and Moclas tic limestone.
The greenstone conglomerate pods in the argillaceous
rocks may have originated as mudflow conglomerates, or may
represent either minor orogenic rejuvenation of the source
areas, or deposition from turbidity currents or slumps.
After the Triassic sediments were deposited, intense
orogenic processes in the thesis area deformed the strata
to such an extent that a major portion of the stratigraphic
section was overturned.
Subsequently, small bodies of
gabbroic rocks were intruded and apparently thereafter, the
Wallowa batholith was emplaced.
Erosion prevailed during the late Cretaceous and
early Tertiary.
By Middle Miocene a mature erosion surface
having a relief of at least several thousand feet existed
in northeastern Oregon,
Th.u'ing the Middle Miocene, ten-
sional. fractures opened throughout the present region of
the Waflova ?'untains and the Columbia River basalt was
e,ttrudad.
Basalt was extruded in quantities to bury the
pra-ezisting topography regionally, creating a relatively
flat plateau surface.
Pxeswnably during the Pliocene, the northern part
of the thesis area was uplifted by normal faulting.
Fault-
ing occurred after the extruion of Columbia River basalt
and prior to Pleistocene glaciation,
Pleistocene glaciation modified most existing topographic features.
Debris derived by recent erosion of the
highlands has filled-in valley floors and built alluvial
fans.
Overall erosion has had little effect on modifying
the topography created during the Pleistocene.
79
ECONOMIC GEOLOGY
Deposits of gold are the only mineralized sites of
economic value in the mapped area.
Mineral deposits dis
cussed in this thesis are gold, limestone, molybdenum and
copper.
[t!
Gold mining (21,
) has been carried on in the Eagle
creek region since the late 1860's.
Lode claims and mines
presently being operated are the following:
Gold Kin2 C,eek claims,
(SW* sec. 16 and SE* sec.
17, T, 6 S., R. k E.)
Two claims which are worked during the summer, are
located along a mineralized fault zone paralleling the Gold
ICing Creek fault.
Adits of the lower claim extend into the
Lower Sedimentary Series, whereas tunnels of the upper claim
are in the Martin Bridge.
Two samples from the upper claim,
one a quartz breccia with sulfide and limonite inclusions,
the other a massive quartz with minor hematite and limonite,
were assayed at $8.00 and $2i6.00 per ton respectively (16).
st Ea2le Mine.
(NE* sec. 32, T. 6 8., R. #3 B.)
Two well kept adits with recent ti1ings are situated
at the base of the siltstone-sandstone unit of the Lower
Sedimentary Series,
mined is unknown.
The vein or mineralized material being
80
0'ian Creek Mine.
(NE* soc. 25, T. 6 S., R. 1*3 B.)
A small strike at the 0 'Brian Mine during the summer
of l99 was the incentive for the development of a road and
the construction of a six-ton mill at the site.
The ore
is found in. coalescing quartz veins which are associated
with basic dikes that intruded the limestones and siltstones.
The mineralized area is small and local,
Buttercup Claim.
(NW* sec. 28, T. 6 5., R. 1f3 B.)
An open pit reveals quartz veins and stringers associated with a basalt dike which intrudes slightly metamorphosed calcax'eous argilhites.
Originally the gold was
found free in. pockets and stringers; but in l99 wiregold in. quartz was found for the first time in. the history
of the claim.
Basin Mine,
(NE* SW* sec. 29, T. 6 S., R. )+3 B.)
According to Gilluly () the veins are all simple
quartz-filled fissures along the joints.
Free gold is
found within the quartz.
Analyses of sandy and shaly limestone near Martin's
Bridge indicate limestone suitable fOr manufacturing
cement (20).
However, the inaccessibility to the small-
sized deposits would not warrant production at the present
time.
[;i1
1lvbdezum
Prospect pits on Hummingbird }buntain occur along the
contact of the batholith. AU pits are in massive bull or
brecciated quartz veins from 3 to l
At the Landis prospect (NE
L)
inches wide.
sec. 6, T. 6 8., R. )lf
the writer did not find any molbdenite; however, at
a pit about 900 yards southeast of the Landis prospect, a
few smal]. flakes of molybdenite were found scattered in a
massive quartz vein 8 inches wide.
No known economic deposits of copper exist in the
thesis area.
Veins of malachite, azurite, and chrysocola
occur along contacts where the Lower Sedimentary Series
has been intruded by Columbia River basalt dikes or small
gabbroic intrusives.
Copper mineralization is found along the ridge between
East Eagle Creek and Bradley Creek.
and narrow.
The veins are short
1.
Baldwin, Ewaxt.
Brothers, 1959.
2.
Chaney B. W. Central Oregon. Sixteenth International
Geological Congress, Washington I). C. Guidebook 21:11932.
3
Ptyfe, 11. 8., F, J. Turner, and .1. Verhoogen.
Geology of Oregon.
136p.
Ann Arbor, Bdwards
Metamorphic reactions and metamorphic tacies. Baltimore,
199. 259p. (Geological Society of America. Memoir
.
Gilluly, James. Geology and mineral resources of the
Baker Quadr
le Oregon, 1937. ll9. (TI. S. Geological Survey.
etin 879)
5.
GilIuly James 3. C Reed, and L F. Park Jr. Some
mining .istrics of eastern Oregon1 1933. ))+Op. (tJ.S.
Geological Survey. Bulletin 81f6-A)
6,
Johnson, Harlan 3.
7.
Kay, Marshall, North AmerIcan geosynclines.
195]..
11f3p. (Geological Society of America.
8.
Keller, W. D. and R. F. Littlefield. Inclusions in
the quartz of igneous and metamorphic rocks. Journal
of Sedimentary Petrology 2O:7-8+. 1950.
9.
Kerr, Paul, Optical mineralogy.
1959.
1+2p.
An introduction to the study of
organic limestones. Quarterly of the Colorado School
of Mines +6:l85,. 1951.
Baltimore
Memoir +8
New York, McGraw-HiU,
lO.T Krauskopt K. F. The Wailowa Batholith.
Journal 1' Science 21l:607_628. 19#3.
American
11. Krumbein, W. C. and L. L. Sloss. Stratigrabj and sedtmentation. San Francisco, W. H. Freeman, 19)6.
'+79p.
12.' Icrumbein, W. C, L. L. Sloss, and B. C. Dapples. Sedimentary tectonic and sedimentary environments. Bulletin of the American Association of Petroleum Geologists
33:1859-1891. ].9tf9,
13/ Kuonen P. H. Significant features of graded bedding.
Bulletin at the American Association of Petroleum
Geologists 37:10+1f-1066.
1953.
83
11i.
Kuenen, P. H. and
A.
Carozzi,
of Geology 62:363-373.
15.
Turbidity currents and
Journal
sliding in geosynclinal basins of the Alps
l93.
Xuenen
P. H. and Henry W. !4enard.
ui'bldity currents,
graded and non-graded deposits. Journal of Sedimentary
Petrology 2283-96. 1952.
16. Lampa, John. Owner of Gold King Creek Claim, Spokane,
Washington. Personal communication. l99.
17.
Lindgren, W
Oregon. U.S.
The gold belt of
Geological
(2J:f5l-776. 1901.
18.
19.
the Blue )untalus
Survey. Annual report
of
22
Mandebaua, Hugo and John Sanford.
Table for computing
thickness of strata measured in a traverse or encountered in a bore bole. Bulletin of the Geological
Society of America 63:765-776.
rriam, John C. A contribution to the geology of
the John flay Basin. University of California PublicatIons in Geological Sciences 2z27O-3l.
1901.
20,
Ikore, Bernard. Non-metallic mineral resources of
eastern Oregon, 1937. p. 133_131+.
(U.S. Gelogica1
Survey. Bulletin 879)
21.
Oregon.
22.
Peacock, M. A.
23.
Pettijohn, F. 3. Determination and calculation of
State Department of Geology and Mineral Resources. Oregon metal mines handbook. Portland,
1939. 125p. (Bulletin ])-A)
and plagonite.
The distinction between chlorophaeite
Geological 1.gazine 67:170-178. 1930.
apher laity values of pebbles
Petrology 6:1+-157.
2r.
25
Pettijohn
Harper,
Plumley
study
F. 3. Sedimentary rocks.
7lSp.
of
Sedimentary
2d ed. New York,
1357.
William.
Black
Hills terrace gravels: A
of Geology 56:
sediment transport. Journal
526-577. l9+8.
26.
Journal
1936.
Prostka, Harold. Structure and petrology of the pmTertiary rocks of the Sparta quadrangle, Oregon. Ph.D.
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27.
Ross, C. P. The geology of part of the Waflowa
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28.
Rubey, W. W. Lithologic studies of fine-grained
Upper Cretaceous sedimentary rocks of the Black Hills
region. 1930. 514p.
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I. C.
Washingou.
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Smith, W. D.
31.
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Triassic of North America. American Journal of Science
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32.
Smith, J. P. Upper Triassic marine invertebrate
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(U.S. Geologi-
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cal Survey..
Professional Paper 11)
33.
Taubeneck, William H, Age of granitic plutons in
eastern Oregon.
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$63p. (Geological Society of America. Special Papers
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4Oóp.
2d
Ma's
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"Algal dust" and the fine-grained vaieties of carboniferous limestone. Geological Magazine
78:192-198. 19+l.
APPENDIX
Plate 2
Fig. I
Lower Sedimentary Series
Gritty sandstone. Plain light
6.+ mm. Diam.
Fig. 2
Lower Sedimentary Series
Laminated silts tone
Note slight bending of laminae on san8/
grain. Plain light
mm. Diam.
Fig. 3
!rtin Bridge formation Marble
Note fibrous pieces of phiogopite
Plain light.
1.6 mm. Diam.
Fig. 1f
Martin Bridge formation Marble
X-ni col
1.6 mm. Diam.
jw.-
-
_.<.
-
-.;
:
Fig. 2
Plate 3
Fig. I
Martin Bridge formation
Laminated calcareous siltatone. Black
laminae contains abundant pyrite. Plain
light. Diam. 6.1+ mm.
Fig. 2
Martin Bridge formation
Bioclastic limestone. Plain light.
Diaa. 6.1+ mm.
Fig. 3
Martin Bridge formation
Calcilutite. Extremely fine-grained
limestone with strips of carbonaceous
material. Plain light. Main. 1.6 mm.
Fig.
Martin Bridge formation
Limestone conglomerate. Cemented by
microcrystalline quartz, calcite, and
greenstone fragments. Plain light.
1+
Diam. 6.1+ mm.
Fig. 1.
1
:-'
Fig. 2
91
Plate )f
Fig, 1
Hrwa1 formation
Calcareous pellets. Note parallel alignPellets composed of cryptocrystalline calcite.
Plain light.
nients,
Dia1.6 mm.
Fig. 2
Hurwal formation
Bioclastjc limestone.
Diam. 1.6 mm.
Plain light.
Fig. 3
Hurwal formation
Marble. Microcrystalline quartz replacing calcite. Plain light.
Diam. 1.6 mm.
Fig.+
Hurwal formation
Marble. X-fljcol,
FIg. 1
FIg, 2
Plate 5
Fig. I
Hurwal formation
Bioclastic limestone. Possible calcareaze
worm tube in the center of photograph.
Plain light. Diam. 6.+ mm.
Fig. 2
Hurwal formation
Calcareous pellets from upper limestone
area. Plain light. Diam. 6?' mm.
Fig. 3
Hurwal formation
Granule limestone and greenstone frag'
menta in matrix of calcite and silt.
Plain light. Diam. 6. mm.
-.
a --------
!'
;
:
L.
.'
1
4
r
.4
II,.
-
9
Plate 6
Fig. 1
Fig. 2
Fig. 3
Hurwa1 formation
Laminated siltstone
Plain light. Diam. 6.
Hurwal formation
Laminated siltatone
Plain 34ght. Diam. 6.
mm.
mm.
Hu.rwal formation
Hierotaulting in laminated siltatono
Plain light. Diam. 6. mm.
Fig. 1F
ITurwal formation
Argiuite.
Light colored bands contain
microcrystalline quartz while dark
bands contain fine-'grained unidentif 1able mafic minerals.
Plain light. Diam. 6.14
,
r.
r
t;
;'
N
I
'
.
97
Plate 7
Fig. I
Columbia River basalt
Labradorite crystal in porpyritic
basalt. X-nicol.
Diam. 1.6 mm.
Fig. 2
Columbia River basalt
Labradorite crystal in aphanitic basalt
X-ni col
Diain. 1.6 mm.
Fig. 3
Quartz diorite
Wefl developed i*yrmekite. Plagioclase
grain at lower left is surrounded by
potash e1dspar. X-niool.
Diam. 1.6 mm.
Fig.
Quartz diorite
Undulating extinction in strained
auartz. X-nicol,
1iam. 1.6 mm.
'.$I .'
,..6
.
.
-
'r.
-:
.:.,
%
g'
iør
w"
'L
/'
,, __.l-
'