The Permian and Triassic 

Seven Devils Group, 

Western Idaho and 

Northeastern Oregon 

G E 0 L 0 G I C A L S U R V E Y B U L L E T I N 1437 

The Permian an~d Triassic 

Seven Devils Group, 

Western ldclho alnd 

Northeastern Oregon 

By TRACY L. VALLIER 

G E 0 L 0 G I C A L S U R V E Y B U L L E T I N 1437 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1977 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Libraiy of Congress Catalog Card No. 77-608195 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D. C. 20402 

St0ck Number 024-001-03020-9 
CO:NTENTS 

Page 

Abstract----------------------------------------------··············.......................................................................... 1 

Introduction·····----------·········-···············-·-············---------·-············-·····-··--·--·-················-············· 1 

Acknowledgments ............................... ........................................................................... 6 

Regional geology .................................... ················--------·········--·-··················-·······--·-············ 6 

Baker quadrangle........................................................................................................... 6 

Riggins region .................................. ..... ......................................................................... 8 

Snake River Canyon ...................... .............................................................................. 9 

Stratigraphy·······-·-·····-----·--------·······-·-············-------··············----·---·-------··········-···········------·-···-·· 10 

Seven Devils Group--·--········----------·-·-·-------·-·--·-·····-·-····---------·--················-··-------·---······ 11 

Windy Ridge Formation ········----··········------···············-····································------ 12 

Hunsaker Creek Formation -·-----··-······------------------···-----·-·-·-··--------··--·············-·· 15 

Wild Sheep Creek Formation --···-·····---·-·----·--···-······----------·-----···············-···----·-- 27 

Doyle Creek Formation ··------···-··--·-····-----------······---------·-----·--··--·--·----·--·--·------···- 36 

Kurry Creek Member ............ ------·······-·-·-·--·--···--···-··-----·-----···-·-----·--······------- 45 

Martin Bridge Umestone ·········----··-----·--·-·-···--------···--···--------------------···-···-······-·-···----- 48 

Hurwal Formation ·····----·--·-··---·--·----··-----···--··-·····---·-··----··-·-·----------------····-··-·--·-·-····-····· 50· 

Coon Hollow Formation ................. ·-----·---·-·········--·--·------·----····-···········--·--·---------······· 50 

Tertiary boulder beds ·······--·----·---····--------·---·-·········----------·-············-····------------·--·········- 51 

Columbia River Basalt Group ----· --·······--··-·--------·--···---·-·--------·--·········-··--··--·----------- 52 

Quaternary deposits -----------··-----·----·--·········-·-·-·----------·--·--------------·-··------····--·-··---·-----·- 53 

Conclusions --········---··-···········-----·-----·-···--·-· ·------------·--------·------------------------··--------------········----·· 54 

References cited .. ·-------···---------·-------·---·------··---------·----·-·--··········----·-·-------·-···········-·······-----······· 56 

ILLUSTRATIONS 

Page 

FIGURE 1. Location map of Snake River Canyon ---------·-----------------------------------·-------- 3 

2. Geologic map of the Snak•~ River Canyon --------·--·------------------------·------- 4 

3. Composite stratigraphic column of pre-Tertiary rocks -------------·------ 10 

4-11. ·Maps showing: 

4. Type section of Hunsaker Creek Formation ---------------·---------·---- 15 

5. Reference section of Hunsaker Creek Formation ------------···----- 16 

6. Type section of Wild :Sheep Creek Formation --------------------·----- 28 

7. Reference section of Wild Sheep Creek Formation·----------------- 29 

8. Type section of Doyle Creek Formation -------------------------------------- 37 

9. Reference section of Doyle Creek Formation ---------------------------- 38 

10. Reference section of Doyle Creek Formation ---------------------·------ 39 

11. Type section of Kurry Creek Member ------------------------------------------ 45 

12. Composite stratigraphie diagram ______ ----------------------------------------------------- 55 

III 
IV CONTENTS 

TABLES 

Page 

TABLE 1. Modal analyses of quartz keratophyre flow rocks from the 

Windy Ridge Formation______________________________________________________________________________ 13 

2. Chemical analyses of quartz keratophyre flow rocks from the 

Windy Ridge Formation______________________________________________________________________________ 13 

3. Quartz keratophyre and spilite chemistries from the Hunsaker 

Creek Formation-------------------------------------------------------------------------------------------- 25 

4. Modal analyses of three spilites, Hunsaker Creek 

Formation ------------------------------------------------------------------------------------------------------ 25 

5. Modal analyses of representative volcanic graywacke, 

Hunsaker Creek Formation ---------------------------------------------------------------------- 26 

6. Modal analyses of representative flow rocks, Wild Sheep 

Creek Formation ------------------------------------------------------------------------------------------ 35 

7. Chemical analyses of representative flow rocks from the 

Whild Sheep Creek Formation __________________________________________________________________ 35 

8. Modal analyses of representative flow rocks from the 

Doyle Creek Formation ------------------------------------------------------------------------------ 43 

9. Chemical analyses of representative flow rocks from the 

Doyle Creek Formation ------------------------------------------------------------------------------ 44 
THE PERl'~IAJ\'" AND TRIASSIC 

SEVEN D~E~VILS GROUP, 

WESTJ~R.N IDAHO AND 

NORTHl~AS'~rERN OREGC•N 

By TRACY L. VALLIER 

ABSTRACT 

Volcanogenic Permian and T1ciassie rocks in the Snake River Canyon of western 

Idaho and northeastern Oregon and in the adjacent Seven Devils Mountains of 

western Idaho are assigned to the Seven Devils Group. New rock-stratigraphic 

units are the Windy Ridge Formation of probable Early Permian age, the Hunsaker 

Creek Formation of Early Permian age, the Wild Sheep Creek Formation of Middle 

and Late Triassic age, and the Doyle Creek Formation of Late Triassic age. The 

Pittsburg Formation of former usage is abandoned, the rocks being renamed the 

Kurry Creek Member and assi~~ned to the newly named Doyle Creek Formation. 

Overlying strata are the Martin Bridge Limestone of Late Triassic age, the Hurwal 

Formation of Late Triassic age, the Coon Hollow Formation of Middle(?) and Late 

Jurassic age, and the Columbia Rilve1r Basalt Group of Miocene age. Underlying 

rocks are assemblages of metagabbro, metamorphosed quartz diorite, metabasalt, 

metadiabase, amphibolite, schist, mylonite, and phyllite that are exposed at The 

Oxbow of the Snake River near Oxbow, Oreg., along a 7-km segment of the Snake 

River south of Pittsburg Langing·, and near the mouth ofthe Imnaha River. Gabbro, 

quartz diorite, and rare granodiorite plutons are concentrated in these assemblages, but some also cut the overlying strata. 

The Seven Devils Group is the result of volcanism, tectonism, and sedimentation 

that occurred within and near volcanic arcs at converging plate boundaries during 

the Permian and Triassic Periods. Large parts of these old arcs probably were 

consumed during later subduction, although direct evidence is lacking in the area 

considered here. 

INTRODUCTION 

The existence of Permian and Triassic rocks in eastern Oregon 

and western Idaho has 1been recognized for many years. Major 

reports that discuss these rocks include those by Lindgren (1901), 

Anderson (1930), Gilluly (19:32, 1937), Ross (1938), Smith and Allen 

(1941), Wagner (1945), Cook (1954), Bostwick and Koch (1962), 

Prostka (1962), Hamilton (196aa, 1963b), Thayer and Brown (1964), 

Stearns and Anderson (1966), Brooks and Vallier (1967), Vallier 

(1968, 1974), and Brooks:, M:cintyre, and Walker (1977). Dissertations and theses concerned with small areas in western Idaho and 

1 
2 SEVEN DEVILS GROUP, IDAHO AND OREGON 

eastern Oregon that are considered to be major contributions to 

this study include those by Wetherell (1960), Prostka (1963), 

Morrison (1964), Nolf (1966), Vallier (1967), Bruce (1971), White 

(1972), and Hendricksen (197 4). 

Rocks of Permian, Triassic, and Jurassic age are among the 

oldest known in extreme western Idaho and northeastern Oregon. 

Farther east, Precambrian rocks of the Belt Supergroup are 

intruded by the Idaho batholith; west of the study area in central 

Oregon, Devonian, Mississippian, Pennsylvanian, and Permian 

rocks have been mapped along the southwestern side of the John 

Day uplift (Merriam, 1942; Merriam and Berthiaume, 1943; Buddenhagen, 1967). The Riggins Group (Hamilton, 1963a), which 

crops out near the western border of the Idaho batholith, may be of 

Paleozoic age, but no fossils have been reported. Lowry (1974, p. 

609) believed that some metamorphic and crystalline rocks in the 

Ironside quadrangle of eastern Oregon are of pre-Devonian age 

(probably Precambrian), but neither fossil nor radiometric ages 

have been determined for these rocks. 

Marine volcanogenic rocks of island-arc origin are dominant in 

Permian and Triassic sequences exposed in the Wallowa Mountains, Snake River Canyon, and the Seven Devils Mountains. 

Relatively new ideas on the evolution of volcanic rocks in mobile 

belts place them at consuming margins of lithospheric plates; 

these rocks may mark ancient subduction zones (Hamilton, 1969; 

Dickinson, 1970; Dewey and Bird, 1970, among many others). The 

following points make a description of the stratigraphic relations 

essential: (1) the proximity of these older island-arc rocks to the 

Idaho and Wallowa batholiths; (2) the fact that they are the 

easternmost exposures of marine Permian and Triassic volcanic 

rocks in western North America; (3) their correlation with rocks of 

similar ages and origins in Nevada, southwestern Oregon, Washington, western Canada, and Alaska; and (4) their probable 

relations to early movements and development of the present 

Pacific Ocean floor. 

This paper describes the stratigraphy of Permian and Triassic 

rocks that are well exposed in the Snake River Canyon of northeastern Oregon and western Idaho and in the adjacent Seven 

Devils Mountains of western Idaho (fig. 1) and proposes six new 

rock-stratigraphic units. 

The geologic map (fig. 2) is simplified from Vallier (1974). A 

small section from the Oregon-Washington border to near the 

mouth of the Grande Ronde River is in part from Glerup (1960) and 

Shumway (1961). Many data are keyed to the map, but because of 

the scale, names of most geographic features and localities could 
INTRODUCTION 3 

.-----------------~llrao _________ ~-----------~·~so ____________ _, 

zlo 

' ..... ...... PENDLETON '.._ .... ..., 

\ 1'1) 

'\~ 

~-'\ 

~ \ 

,... \ 

~ \ ~ \ 

0 \ 

~ e\BAKER 

' ' 

0 25 50MILES 

0 25 50KILOMETERS 

il~ CJ>'•Moscow 

~I /CLEARWATER RIVER 

L~ / 

I 

<!l,::z: ~~a 

~:LEARWATER 

SALMON 

BOISE 

• 

'\ 

',, 

~ID 

RIVER 

MTS 

..... , 

' 

~~~ ~------------------L---------~-----------~--------------~ 

FIGURE 1.-l.Alcation map of the Snake River Canyon, northeastern Oregon, 

western Idaho, and southeastern Washington. 

not be included. The reader is encouraged to refer to the topographic maps that served as bases for the geologic map. These 

include (south to north) Copperfield, Homestead, Cuprum, He 

Devil, Kernan Point, and Imnaha 15-minute quadrangles and 

(south to north) the Kirkwood Creek, Grave Point, Wolf Creek, 
4 SEVEN DEVILS GROUP, IDAHO AND OREGON 

FIGURE 2.-Geologic map of the Snake River Canyon. 

Cactus Mountain, Deadhorse Ridge, Wapshilla Creek, and Jim 

Creek Butte 7V2-minute quadrangles. 

Most data reported here were gathered during the 1964, 1965, and 

1968 through 1971 field seasons with additional short trips into the 

area during the spring of 1973 and the summers of 1974 and 1975. 

The stratigraphic sequences were partly described by Morrison 

(1963) and Vallier (1967), who mapped the northern and southern 

parts of the Snake River Canyon, respectively, within the study 

area. Mapping subsequently has been extended by the author to 

include all of the Snake River Canyon north of Oxbow, Oreg., to the 

mouth of the Grande Ronde River and parts of the adjacent Seven 

Devils Mountains and Salmon River Canyon of western Idaho. 

Several thousand meters of stratigraphic section, measured and 

described during the fieldwork, were complemented by studies of 

more than 600 thin sections plus X-ray diffraction, X-ray fluorescence, atomic absorption, and electron microprobe investigations. 
INTRODUCTION 

SCALE 

181 .. o=:5""'==-..i:::=-oi::::::J....i::=:::&a10 KILOMETERS 

z 

I.LJ 

~ 

FIGURE ~:.-Continued. 

loXPLfl,NATION 

c~ Columbia Riv'ar Basalt Group 

Unconformity 

~~ Intrusive rocks 

[lli~ r ·~-·.;r·· 

Coon Hollow Formation 

u~ Older intrusive rocks 

Unconformity 

IIi~ ~ 

Martin Brid9e Limestone 

Jncorliormity 

~~ Doyle Cree' Formation 

~~ Wild Sheep Creek Formation 

Unconiormity 

~SJ Hunsaker Cret~k Formation 

Unconformity(?) 

~::] Windy Formation 

Basement CIJmplex of 

metamorphic and plutonic rocks 

5 

l 

_(TERTIARY 

> CRETACEOUS 

~ JUR~~SIC 

~JURASSIC J 

} JURASSIC 

OR 

TRIASSIC 

TRIASSIC 

l 

f PERMIAN 

J 

l J PERMIAN(?} 

Contact, approximately located 

-i~- High- angle thrust fault 

~~ Low - angle thrust fault 
6 SEVEN DEVILS GROUP, IDAHO AND OREGON 

Fossils were identified by F. G. Stehli (Permian), N.J. Silberling 

(Triassic), and R. W. Imlay (Jurassic). 

Rocks are dominantly volcanic, with both flow and clastic rocks 

represented. The term volcaniclastic is used for clastic volcanic 

rocks whose origin, that is, pyroclastic or epiclastic, is not known. 

Otherwise, these rocks are named according to their origin and 

grain size, for instance lapilli tuff and graywacke. Although the 

Permian and Triassic rocks have undergone low-grade (greenschist) metamorphism, they will generally be referred to according 

to the original rock type for convenience. An exception is made in 

descriptions of flow and shallow hypabyssal rocks from stratigraphic sections where thin section studies were used to complement the fieldwork. In these descriptions, for example, the rock 

names quartz keratophyre and keratophyre are used for metamorphosed high-sodium rhyolite, dacite, and andesite, and spilite 

is the name used for metamorphosed high-sodium basalt and 

basaltic andesite. 

ACKNOWLEDGMENTS 

It is not possible to list all the people who have assisted me with 

this project. However, some have been outstanding with their 

encouragement, enthusiasm, and knowledge of adjacent regions 

which they shared freely. These include Howard Brooks, George 

Walker, W. H. Taubeneck, R. E. Corcoran, C. Field, David Bostwick, T. Thayer, Bruce Nolf, Rolland Reid, and Hollis Dole. Others 

who have contributed considerable time and effort are David L. 

White, David Fredley, Ron Ozier, Jim Waldrip, Stan Shimer, Willis 

H. White, N. S. Wagner, and Rodey Batiza. 

Funds, equipment, and space provided by the National Science 

Foundation, Geological Society of America, Sigma Xi, Oregon 

Department of Geology and Mineral Industries, Idaho Bureau of 

Mines and Geology, Indiana State University, and the University 

of California at San Diego are gratefully acknowledged. 

REGIONAL GEOLOGY 

Pre-Tertiary rocks in northeastern Oregon and westernmost 

Idaho are exposed as inliers in a Cenozoic cover. Pre-Tertiary rocks 

within this region have been well described: the Baker 30-minute 

quadrangle by Brooks, Mcintyre, and Walker (1977) and the 

Riggins area by Hamilton (1963a). The area included within the 

Wallowa Mountains, Seven Devils Mountains, and Snake River 

Canyon is described in this report. 

BAKER QUADRANGLE 

In the Baker region, the oldest reported stratified rocks (Taube-
REGIONAL GEOLOGY 7 

neck, 1955) are metamorphosed argillite, chert, lava, tuff, and 

limestone that overlie and are tectonically mixed with metamorphosed gabbro, diabase, quartz diorite, and ultrarrtafic rocks. This 

rock association is similar to that reported f1ron1 a modern-day 

oceanic crustal section. Stratified rocks are the Elkhorn Ridge 

Argillite, Burnt River Schist, and Nelson Marble (Gilluly, 1937; 

Prostka, 1962). Many problems remain concerning the ages of 

these rocks. For example, lim.estone bodies in the Elkhorn Ridge 

Argillite have yielded Pennsylvanian and Early Permian fusulinids (D. A. Bostwick, oraJ commun., 1975), yet J\1iddle Triassic 

radiolarians were reported from cherts that are associated with 

these limestone blocks in an area southwest of John Day, Oreg. 

(Jones, oral comm., 1977). W'ith the inconclusive age data now 

available, it is possible to conclude that the Paleozoic limestone 

bodies are allochthonous blocks in a melangelike unit that tectonically accumulated in the Triassic. 

Upper Triassic (Karnian) volcanic rocks crop out in the southern 

part of the Baker quadrangle near Huntington, Oreg., and also 

east of the Snake River Canyon in the Sturgi11 Peak and Cuddy 

Mountain areas of western Idaho. Correlative Upper Triassic 

rocks are exposed in the Snake River Canyon north of Oxbow, 

Oreg., and in the Seven Devils and Wallowa Mountains. Lower and 

Middle Jurassic flyschlike sedimentary rocks are known to overlie 

the Karnian volcanic rocks just north of Huntington; however, 

some of the sedimentary section may be of Late Triassic age in the 

thicker parts of the exposed sequence (H. C. Brooks, oralcommun., 

1975). The youngest pre-Tertiary rocks recognized in the region are 

black mudstone of Late Jurassic (lower Callovian) age exposed at 

Mineral, Idaho. 

The older metamorphosed plutonic rocks that are tectonically 

associated with the Elkhorn Ridge Argillite and Burnt River 

Schist are most likely basement rocks upon which the stratified 

rocks were deposited. Ages of basement rocks are unknown but 

could include rocks that crystallized at any time in the Pennsylvanian to Late Jurassic interval. Small quartz diorite and 

granodiorite plutons were intruded during the Late Jurassic and 

Early Cretaceous Epochs, and regional metmnorphism culminated sometime between the deposition of Late Jurassic Callovian 

sediments and the intrusion of these young plutons. Characteristic of the pre-Tertiary structure throughout 1nost of the Baker 

quadrangle is the division of the rocks into east- and northeasttrending belts that have parallel fold axes and faults. Some rocks 

have been folded at least twi~e along nearly parallel trends. In 

contrast, the Triassic and Jurassic strata near Huntington have 

undergone only one deformation. 
8 SEVEN DEVILS GROUP, IDAHO AND OREGON 

RIGGINS REGION 

In the Riggins region, bordered on the west by the crest of the 

Seven Devils Mountains and on the east by the Idaho batholith, 

Hamilton (1963a) described the Riggins Group, a thick sequence of 

rocks that may be older than the Permian and Triassic Seven 

Devils Group (Seven Devils Volcanics of Anderson, 1930) exposed 

in the adjacent Seven Devils Mountains and Snake River Canyon. 

The Riggins Group is divided into four formations in ascending 

order: the Fiddle Creek Schist, made up of metamorphosed silicic 

tuffs and lavas; the Lightning Creek Schist, composed of meta-

·morphosed mafic and silicic tuffs and lavas; the Berg Creek 

Amphibolite; and the Squaw Creek Schist, which consists of metamorphosed sedimentary rocks. The Riggins Group has been thrust 

over the Seven Devils Group along the Rapid River thrust. 

Hamilton (1963a, b) believed that the Riggins Group might 

reasonably be correlated with rocks of any age from Cambrian 

through Early Cretaceous. 

From reconnaissance field studies in both the Riggins and Baker 

areas, at least three alternative hypotheses can be considered for 

the age and origin of the Riggins Group: (1) It is completely 

unrelated to any other rocks in northeastern Oregon and western 

Idaho; (2) it is equivalent to the Seven Devils group but is a 

metamorphosed and greatly deformed facies that was telescoped 

along the Rapid River thrust and other faults both before and 

during the intrusion of the Idaho batholith; or (3) it is correlative 

with the Burnt River Schist, Elkhorn Ridge Argillite, and the 

Jurassic sedimentary rocks of the Baker region. I prefer the last 

hypothesis, but additional fieldwork certainly is necessary to solve 

this problem. 

The Squaw Creek Schist retains evidence of flyschlike sediments 

similar to the Jurassic shale and argillite in the Baker quadrangle, 

even though it was greatly affected by metamorphism and deformation during the intrusion of the Idaho batholith. The northeasterly structural trends of the pre-Tertiary rocks in the Baker 

quadrangle can be projected beneath the Cenozoic cover into the 

Riggins area. Therefore, the Fiddle Creek and Lightning Creek 

Schists might be correlative with the Elkhorn Ridge Argillite and 

Burnt River Schist, and the Squaw Creek Schist could be correlative with the Jurassic clastic assemblage. The Berg Creek 

Amphibolite probably is a metamorphosed (by the Idaho batholith) ultramafic and mafic assemblage that lies between the older 

Fiddle Creek and Lightning Creek Schists and the younger Squaw 

Creek Schist. In addition, ultramafic rocks separate the older rocks 

(Fiddle Creek and Lightning Creek Schists) from the Squaw Creek 
REGIONAL GEOLOGY 9 

Schist near the Salmon River bridge just north of Riggins, Idaho. 

In the Baker quadrangle, pods of ultramafic and mafic rocks 

similarly occur along the suture between the Elkhorn Ridge 

Argillite, Burnt River Schist and associated plutonic rocks, and the 

Jurassic clastic assemblage. 

Hamilton (1976) stated that the suture in the Riggins Group 

marks the collision of the Sf~ven Devils ensirr.Latic island arc with 

the continent during late Permian or Triassic tirne. He regards the 

Squaw Creek Schist as part of a melange, the ultramafic rocks and 

adjacent Lightning Creek Sehist as an ophiolite assemblage, and 

the rest of the Lightning Creek and Fiddle Cr·eek Schists as a 

volcanic arc assemblage. 

SNAKE RIVER CANYON 

Pre-Tertiary stratigraphy in the Snake River Canyon (fig. 3) is 

similar to sequences in the Wallowa and Seven Devils Mountains, 

the southern part of the Baker quadrangle nea:r Huntington, Oreg., 

and the Cuddy Mountain area. In the Snake Riv1er Canyon, rocks 

of Early Permian, Middle and Late Triassic, and Middle and Late 

Jurassic age were deposited in island-arc environments. The 

Upper Triassic limestone and associated shale units formed as 

platform carbonate and basin deposits over a large part of the 

region. Jurrassic flyschlike black shale and sandstone units 

probably are related to deposition in basins associated with the 

arc. Low-grade regional metamorphism culmLinated after deposition of Upper Jurassic marine sediments and before the intrusion 

of some bodies of gabbro and quartz diorite; however, plutonism 

was common both before and after culminating metamorphism. 

Structural trends are northeast-southwest and northwest-southeast, with most deformation exemplified by hi:gh-angle reverse 

faults, some of which also had strike-slip movernent. 

Some of the rocks upon which the Permian and Triassic strata 

were deposited are exposed in the Snake River Canyon near 

Oxbow, south of Pittsburg Landing, and east of the Imnaha River 

mouth. These rocks represent older metamorphic and plutonic 

terranes that, subsequent to their de~velopment, were covered by 

Permian and Triassic strata and intruded by younger plutons 

related to both the Late Triassic and Latf~ Jurassic to Early 

Cretaceous intrusive events .. Wide shear zones 'vithin these complexes are marked by mylonitic rocks, amphibolite, hornblende 

and chlorite schists, gneiss, and phyllite. Ages probably range 

from pre-Permian to at least the Late ~Jurassic or Early Cretaceous. 

Details of the tectonic, plutonic, and metamorphic histories have 

not yet been determined. 
10 

7500 

5000 

4500 

4000 

3500 

1500 

0 

SEVEN DEVILS GROUP, IDAHO AND OREGON 

COMPOSITE STRATIGRAPHIC COLUMN 

NAME AND DESCRIPTION 

Columbia River Basalt Group: basalt flows 

Coon Hollow Formation: mudstone; sandstone; rare breccia; 

and conglomerate 

Hurwal Formation: shale and limestone, exposed near mouth 

of the Grande Ronde River 

Martin Bridge Formation: limestone and rare dolomite 

Doyle Creek Formation: conglomerate; epiclastic breccia, 

sandstone, and shale; pyroclastics; metabasalt and keratoPhyre 

Wild Sheep Creek Formation: metabasalt; meta-andesite; 

keratophyre; tuff; conglomerate, breccia, sandstone; and 

argillite 

Hunsaker Creek Formation: pyroclastic breccia; tuff; conglomerate; breccia; sandstone; argillite; rare limestone; keratophyre and spilite flows 

Windy Ridge Formation: keratophyre flows and tuff 

Basement rocks: amphibolite, metagabbro, meta quartz, 

diorite, hornblende schist; mylonite, gneissic mylonite; 

exposed at Oxbow of the Snake River, south of Pittsburg 

Landing, and near the mouth of the Imnaha River 

FIGURE 3.-Composite stratigraphic column of pre-Tertiary rocks in the Snake 

River Canyon north of Oxbow, Oreg. 

STRATIGRAPHY 

Major stratigraphic units in the Snake River Canyon, Wallowa 

Mountains, and Seven Devils Mountains are Permian and Triassic 

volcanogenic rocks, Triassic limestone, Triassic and Jurassic 

shale and sandstone, Miocene plateau basalt, and Quaternary 

deposits (fig. 3). The _Permian and Triassic volcanic rocks in the 

Snake River Canyon are assigned to the Seven Devils Group 
STRATIGRAPHY 11 

(redefined) which includes four formations and one member. These 

are the Lower Permian(?) \\rindy Ridge Fornlati[on (new name), 

Lower Permian Hunsaker Creek For1nation (new name), Middle 

and Upper Triassic Wild Sheep Creek Formation (new name), and 

the Upper Triassic Doyle Creek For:mation (new name), which 

includes the Kurry Creek Member (new name). These volcanogenic 

rocks are capped by the Upper Triassic Martin BJtidge Limestone, 

which in turn is overlain by the Upper Triassic Hurwal Formation 

(the Hurwal Formation in the Wallowa Mountains is in part 

equivalent to the Lucile Slate in the Seven Devils region), and the 

Middle and Upper Jurassic Coon Hollow Forrnation. Miocene 

basalt caps the pre-Tertiary sequence, and (~uaternary glacial, 

landslide, and alluvial unconsolidated deposits locally mantle the 

older rocks. 

Because of extensive structural complications, pre-Miocene deep 

erosion, and rapid lithofacies changes:, particularly in the volcanogenic Seven Devils Group, thicknesses of the units are not 

accurately known; exposed contacts are generally tectonic rather 

than stratigraphic. The composite stratigraphic column for the 

Snake River Canyon shown in figu1~e 3 is derived from many 

measured sections but is really a best estimate for thicknesses 

which may be as much as 30 percent off for some units. 

SE VE.:\1 DEVILS GROUP 

Previous workers generally have followed the terminology of 

Anderson (1930) by referring to the chiefly metavolcanic rock 

sequences in the Snake River Canyon and Seven Devils Mountains 

as the "Seven Devils Volcanics." The name "Seven Devils Group" 

is here substituted for the "Seven Devils Volcanics" and is defined 

to include four newly nan1ed formations: Windy Rildge Formation, 

Hunsaker Creek Formation, Wild Sheep Creek Formation, and 

Doyle Creek Formation. The type area for the Seven Devils Group 

is in the Seven Devils Mountains and the adjacent Snake River 

Canyon of western Idaho, Idaho County, He Devil and Cuprum 15-

minute quadrangles. The Seven Devils Group includes rock sequences that are lithologically and chronologically similar to the 

Clover Creek Greenstone (GiHuly, 1937; Ross, 19:38) and "Lower 

Sedimentary Series" (Smith and Allen, 1941, p. 8 and 9) that are 

well exposed in the Wallow a 1\iountain:s. Its upper part can also be 

correlated with part of the Upper Triassic voleanic sequence 

exposed along both sides of the Snake River near Huntington, 

Oreg., and with the Upper Triassic volcanic flow and volcaniclastic rocks in the Cuddy Mountain area. 
12 SEVEN DEVILS GROUP, IDAHO AND OREGON 

WINDY RIDGE FORMATION 

The name Windy Ridge Formation is here given to a sequence of 

metamorphosed silicic volcanic flow and volcaniclastic rocks 

exposed along the south end of Windy Ridge, across the Snake 

River from Oxbow, Oreg. (fig. 2). Because of poor exposures, 

indistinct bedding, structural complications and a large number of 

mafic dikes, no stratigraphic section could be measured. The best 

exposures, designated the type locality, are along the Idaho Power 

and Light Company road on the east side of the Snake River in 

sees. 8 and 17, T.19 N., R. 4 W., Idaho, north of the bridge at Oxbow. 

Elsewhere, exposures are very poor and are characterized by 

scattered, deeply weathered brown-stained outcrops. 

The Windy Ridge Formation is easily distinguished from 

younger formations; it is dominantly grayish-green quartz keratophyre tuff, quartz keratophyre tuff-breccia, and quartz keratophyre flows. No definitely epiclastic rocks occur, and it is 

concluded that the formation is entirely flow and pyroclastic rocks. 

This paper follows Schermerhorn's (1973) recommendation that 

the name "keratophyre" be applied to light-colored sodic intermediate albite porphyritic volcanic rocks and that the name 

"quartz keratophyre" be applied to leucocratic sodic felsic quartzalbite porphyritic or albite porphyritic volcanic rocks. His conclusion that most keratophyric rocks are in reality quartz keratophyre is strengthened by this study. 

Porphyritic quartz keratophyre flow rocks have porcellaneous 

luster and conchoidal to subconchoidal fracture. Euhedral white 

phenocrysts of albite and partially resorbed phenocrysts of quartz 

0.5-4.0 mm in diameter are set in a light-grayish-green silicified 

groundmass. In thin section, quartz phenocrysts show bipyramidal to completely rounded shapes, the latter due to magmatic 

resorption. Albite phenocrysts generally are clear but rarely show 

clouding due to replacement by fine-grained epidote and white 

mica. Primary mafic phenocrysts are absent, although chlorite 

replaces rare amphibole grains. Abundant quartz spherulites 

probably replace original glassy spherulites and variolites. 

Groundmass minerals are quartz, albite, chlorite (penninite), 

sphene, leucoxene, epidote, white mica, and rare hematite and 

calcite. The chlorite is responsible for the grayish-green color. 

Modal analyses of four quartz keratophyre flow rocks are given in 

table 1, and chemical analyses of two quartz keratophyre flow 

rocks are given in table 2. Chemical analyses of the quartz 

keratophyre flow rocks show relatively high amounts ofSi02 and 

Na2 0 and low FeO, Fe20 3 , MgO, and CaO. Particularly signifi-

14 SEVEN DEVILS GROUP, IDAHO AND OREGON 

stratified. Few bedding planes are apparent, and grading is rare. 

Clasts range from sand size to as much as 3 em in diameter. All 

clastic rocks are composed of debris from a monolithologic quartz 

keratophyre and keratophyre source. Major components are quartz 

keratophyre and keratophyre rock fragments, quartz, albite, and 

recrystallized pieces of pumice set in a quartz and albite matrix. 

The base of the Windy Ridge Formation is not exposed. The 

lower part of the formation is sheared and apparently is tectoncally mixed with underlying metamorphic and plutonic rocks of 

the Oxbow-Cuprum shear zone (Taubeneck, 1966, p. 2118), a 

tectonic-stratigraphic-plutonic unit that is well exposed in an area 

extending from Oxbow Dam northeast along Indian Creek to and 

beyond Cuprum, Idaho. The Oxbow-Cuprum shear zone consists of 

mylonite, gneissic mylonite, amphibolite, hornblende schist, plagiogranite (low-potassium trondhjemite, quartz diorite, and albite 

granite), metagabbro, metadiabase, and metabasalt. Tectonite 

fabrics parallel the northeast-trending shear zones, faults, and 

dikes. The Windy Ridge Formation probably was deposited on 

older plutonic rocks and· subsequently incorporated tectonically 

during shearing and recrystallization. 

The top of the Windy Ridge Formation also is difficult to map 

because of faulting. Along the northwest side of Windy Ridge, the 

formation is separated from the overlying Lower Permian Hunsaker Creek Formation by a high-angle fault. Elsewhere, along the 

central part of Windy Ridge, the boundary between the two 

formations was drawn where the grayish-green flow and volcaniclastic rocks of the Windy Ridge Formation are overlain either by a 

conglomerate or a mafic breccia of Hunsaker Creek lithology. This 

contact may be either an unconformity or a fault, but definite 

relations could not be established. Thickness of the Windy Ridge 

Formation is estimated at 500 m. 

The Windy Ridge Formation is not known to crop out at any 

other place in northeastern Oregon and western Idaho and seems 

to be a local accumulation of silicic volcanic rocks, possibly 

associated both in time and space with the older plagiogranites of 

the Oxbow-Cuprum shear zone. Thereisnoevidencethatindicates 

whether eruptions were subaerial or submarine. The presumed 

high viscosity of the magma suggests that eruptions were very 

local and the deposit may in part represent a local lava and tuff 

dome. The rocks apparently were erupted prior to the deposition of 

the Lower Permian Hunsaker Creek Formation, but because of 
STRATIGRAPHY 15 

petrologic similarities between keratophyric rocks in both formations, it is possible that the Windy Ridge Formation is a lithofacies 

of the lower part of the Hunsaker Cr«~ek Formation. Until fossil or 

radiometric dates are available, the Windy Ridge Formation is 

considered to be either equivalent to or older than the Hunsaker 

Creek Formation and of probable Early Permian age. Therefore, 

these may be the oldest known volcanic rocks in a developing 

Permian island arc. 

HUNSAKER CREEK FORMATION 

The Hunsaker Creek Formation is here named for a thick 

sequence of metamorphosed strata exposed along the Snake River 

Canyon for nearly 15 km north of Oxbow and in the southeastern 

part of the Wallowa Mountains. Best exposures are in the Snake 

River Canyon, particularly eanyons of tributary creeks including 

Hunsaker, Homestead, Herman, and Ballard Cr~eeks, which enter 

the river from the Oregon side. 

The type section (fig. 4) is designated as lying between the eleva0 1 MILES 1-------,.--....__-, 

0 2 Kl LOMETEFtS 

FIGURE 4.-Type section of the Hunsaker Creek Formation. Base from U.S. 

Geological Survey Copperfield 15-minute quadrangle, 1:62,500, 1957. 
16 SEVEN DEVILS GROUP, IDAHO AND OREGON 

tions of 650 and 1,060 m (2,100 and 3,500 ft) on the north side of 

Hunsaker Creek, the first creek along the Oregon side of the river 

north of the town of Oxbow. The section is in the SW% sec. 5 and 

the NE% sec. 6, T. 7 S., R. 48 E., Copperfield 15-minute quadrangle. 

Neither the stratigraphic top nor the base of the formation is 

exposed in the type section, but it is considered to be most suitable 

because of the small amount of deformation, the thickness exposed 

(785 m), and the ease of access. Farther north at Ballard Creek a 

reference section (fig. 5) measures 676 m. 

R.48E. 

0 

I 

0 

1 ·MILES 

I I 

2 KILOMETERS 

R.4W. 

FIGURE 5.-Reference section of the Hunsaker Creek Formation along the north 

side of Ballard Creek. Base from U.S. Geological Survey Homestead 15-minute 

quadrangle, 1:62,500, 1957. 
STRATIGRAPHY 17 

Type section, Hunsaker Creek Formation 

Location: Copperfield 15-minute quadrangle, SW1!, sec. 5 and NE% sec. 6, T. 7 S., R. 48 E.; along north side of 

Hunsaker Creek between elevations of 650 and 1,060 m (2,100 and 3,500 ft); Hunsaker Creek is the first major 

creek north of Pine Creek near the town of Oxbow, Oreg.; descriptions aided by thin-section petrography of35 

rocks; measured by Jacobs Staff method. Deeply eroded rocks of the Hunsaker Creek Formation form the top 

of the measured section. Exact part of the formation is not known but most likely the section is near the base. 

Unit 

33. 

32. 

Description 

Spilite, greenish-black; weathers to dark-yellowish brown; 

fine grained, amygdaloidal:; individual flows 3-5m thick; 

forms rugged outcrops ............................................................... .. 

Volcanic siltstone (keratophyre tuff?), pale-green; weathers 

moderate yellowish brown; poorly sorted; angular grains; 

pebbly, silicified, and recrystallized matrix; graded in 

beds 30-70 em thick ................................................................. ____ _ 

31. Volcanic sandstone and volcanic siltstone, pale-red; weathers pale yellowish brown; graded beds 0.25-2 m thick; 

Cumulative thickness 

above base of section 

(m) 

785 

758 

poorly sorted; angular fragments; probably tuffaceous. 745 

30. Volcanic siltstone, grayish-olive; weathers pale yellowish 

brown; thin bedded; poorly sorted; pebbly; some grading 739 

Fault; break in section 

29. Volcanic siltstone, grayish-olive; weathers moderab~ yellowish brown; some grading; pebbly; poorly sorted; beds 

10-90 em thick ..... _________ , _____ .. ______________________________ ........................... 697 

28. Conglomerate, dark-greenish-gray; weathers yellowish 

brown; pebble to cobble size with some irregular blocks 

from 1 to 2 m in diameter; poorly sor1ted; weakly graded 

in beds 7-10 m thick, with thin siltstone beds at top of 

graded units; spilite and keratophyre clasts dominant __ 689 

27. Volcanic sandstone (keratophyre tuff?), grayish-green; 

weathers pale yellowish brown; grades to siltstone in 

2-3-m-thick beds; moderate to poor sorting; crystals 

mostly feldspar; scattered pebbles up to 2 em in diameter; 

faint cross-laminations in some beds ............. ________________ .. _____ 647 

26. Volcanic siltstone, grayish-olive; weathers light olive 

brown; silicified and recrystallized; :sand in some thin 

beds 1-2 em thick ......................... _____________ ..................... ----- _________ 615 

25. Volcanic sandstone (keratophyre tuff?), grayish-green; 

weathers pale yellowish brown; graded beds 0.5-1.5 m 

thick; coarse to fine grained; some beds moderately well 

sorted; faint cross-laminations ________________ .. _________ .. ____________ .. ___ 609 

24. Conglomerate, grayish-olive; weathers pale yellowish 

brown; pebble to cobble sizes 3-30 em in diameter; clasts 

subrounded, composed of spilite, keratophyre, and volcaniclastic rocks ............................. __________ .. ___________ .... __________ _________ 593 

23. Volcanic sandstone (keratophyre tuff?), grayish-olive; 

weathers light olive brown; poorly sorted; graded from 

coarse sand to coarse silt sizes; forms rugged cliffs ________ 583 

22. Spilite, dusky-yellow-green; weathers moderate yellowish 

brown; fine grained; amygdaloidal; may be a sill; deeply 

weathered outcrop .................... ____________________________ .. ____________ _________ 570 
18 SEVEN DEVILS GROUP, IDAHO AND OREGON 

Type section, Hunsaker Creek Formation-Continued 

Unit Description Cumulative thickness 

21. Volcanic sandstone (keratophyre tuff?), dusky-yellowgreen and brownish-gray; weathers moderate yellowish 

brown; graded to siltstone in beds 0.3-1.5 m thick; pebbly 

in some beds; poorly sorted; angular grains, some 

above base of section 

(m) 

matrices silicified -------------------------------------------------------------------------- 567 

20. Volcanic siltstone with some sandstone, breccia, and conglomerate, pale-grayish-green; weathers pale yellowish 

brown; graded beds; some tuffaceous; individual beds 

0.5-2.0 m thick-------------------------------------------------------------------------------- 543 

19. Conglomerate with some volcanic breccia and sandstone 

beds, pale-green; weathers pale yellowish brown; some 

grading; bedding planes poorly defined; in part pebbly 

mudstone; cut by 2-m-thick diabase dike near top; clasts 

in conglomerate mostly keratophyre with some spilite 

and volcaniclastic rocks______________________________________________________________ 500 

18. Spilite tuff-breccia, greenish~black; weathers dark yeliowish brown; poorly sorted; some interfingering spilite 

flows 1-2m thick; deeply weathered; rounded outcrops.. 474 

17. Volcanic sandstone (keratophyre tuff?), pale-green; weathers pale yellowish brown; weak grading; poorly sorted; 

interbedded with some volcanic siltstone ---------------------------- 458 

16. Spilite, dusky-yellow-green; weathers moderate brown; 

porphyritic with phenocrysts of feldspar up to 2 mm in 

diameter; deeply weathered; may be intrusive.................... 449 

15. Volcanic breccia (keratophyre tuff breccia?), pale-green; 

weathers pale yellowish brown; poorly sorted; angular 

fragments 0.5-5 em; keratophyre clasts; silicified matrix 442 

14. Volcanic siltstone (keratophyre tuff?), pale-green; weathers 

pale yellowish brown; silicified matrix__________________________________ 426 

13. Volcanic breccia; same as unit 15 ---------------------------------------------- 422 

12. Volcanic breccia and volcanic sandstone, tuffaceous(?); 

greenish-gray; weathers pale yellowish brown; graded 

beds 3-5 m thick; poorly sorted, angular fragments; 

feldspar rich; largest clasts 5 em in diameter; outcrops 

form rounded shoulders -------------------------------------------------------------- 415 

11. Spilite, greenish-black; weathers moderate brown; fine 

grained; may be intrusive ---------------------------------------------------------- 392 

10. Volcanic breccia and volcanic sandstone; same as unit 12 388 

9. Volcanic sandstone (keratophyre tuff?), grayish-green; 

weathers pale yellowish brown; some grading to coarse 

silt sizes; poorly sorted; angular fragments up to 2 em in 

diameter in a sand matrix; recrystallized matrix-------------- 353 

8. Volcanic siltstone, grayish-green; weathers pale yellowish 

brown; weak grading; silicified matrix__________________________________ 310 

7. Volcanic breccia (keratophyre tuff breccia?), grayish-olive; 

weathers pale yellowish brown; graded to coarse sandstone in beds 2-3 m thick; clasts in breccia up to 6 em in 

diameter; poorly sorted---------------------------------------------------------------- 302 
STRATIGRAPHY 19 

Type section, Hunsaker Creek Formation-Continued 

Unit Description Cumulative thickness 

above base of section 

(m) 

Fault; break in section 

6. Spilite, greenish-black; weathers moderate brown; porphyritic with phenocrysts up to a mm in diameter:; amygdaloidal...................................................................................................... 291 

5. Volcanic breccia, sandstone, and siltstone (pyroclastic?), 

grayish-green; weathers pale yellowish brown; graded 

beds 0.3-2.0 m thick; angular fragments; poody sorted.. 289 

Diabase dike cuts section here 

4. Volcanic sandstone (keratophyre tuff?), grayish-gre•en; 

weathers yellowish brown; poorly sorted; graded from 

coarse to fine sand in beds 0. 7-2.0 m thick; abundant 

rock (keratophyre) fragments..................................................... 275 

3. Volcanic sandstone (keratophyre tuff?), volcanic breccia, 

and quartz keratophyre flows, grayish-green; weathers 

pale yellowish brown; graded sequence ofbreceia to sandstone; poorly sorted; recrystallized and silicified matrixes; 

individual graded beds from 1.5 to 15m thick; interbedded 

quartz keratophyre flows o:f same composition as volcaniclastic rocks---------------------·-----------------------------------------------·----- 264 

2. Quartz keratophyre, yellowish-brown; weathers grayish 

orange; porphyritic; phenocrysts 1-3 m in diameter of 

plagioclase (albite) and quartz -------------·-······------··---------·----·----- 94 

1. Conglomerate, grayish-green,. weathers pale yellowish 

brown; poorly sorted, clasts 0.5-6.0 em in diameter, well 

rounded; beds grade to volcanic siltstone; clasts are 

quartz keratophyre (60 perc,ent), spilite (7 percent), and 

volcaniclastic rocks (33 percent)-------------------------·--------------·----- 24 

Base is not exposed; basalts of the Columbia River Basalt Group 

overlap the section. 

Total thickness of the exposed part of the Hunsaker Creek Formation is 785 m. 

Reference section, Hunsaker Creek Formation 

Location: Homestead 15-minute quadrangle, W1/2 sec. 11, T. 6 S., R. 48 E.; along north side of Ballard Creek 

between elevations of 640 and 1,100 m (2,100 and 3,600 ft); Ballard Creek is at the north end of the road that 

follows the Snake River on the Oregon side:. a power-line road begins near the mouth of Ballard Creek. 

Descriptions aided by studies of 30 thin sections; measured by tape and Brunton and Jacobs Staff methods. 

Deeply eroded rocks of the Hunsaker Creek Formation form the top of the measured section. Exact part of the 

formation is not known but most likely the s·~ction is near the top. 

Unit 

48. 

Description 

Volcanic siltstone (keratophyre tuff?)1, grayish-grElen; 

weathers pale yellowish brown; graded from fine sand to 

fine silt in beds 0.3-1.0 m thick; poorly sorted; silicHied 

and recrystallized matrices·--·-··-----·---------··---··---·-------·--·--····· ..... . 

Cumulative thickness 

above base of section 

(m) 

676 
20 SEVEN DEVILS GROUP, IDAHO AND OREGON 

Reference section, Hunsaker Creek Formation-Continued 

Unit Description Cumulative thickness 

47. Volcanic breccia and volcanic sandstone, pale-green; 

weathers pale yellowish brown; graded beds 0.5-2.0 m 

thick; poorly sorted; rock fragments mostly chloritized 

above base of section 

(m) 

mudstone clasts.............................................................................. 672 

46. Volcanic sandstone (keratophyre tuff?), dusky-yellowgreen; weathers pale yellowish brown; graded beds 1.2-

3.0 m thick; upper 2 m is siltstone; poorly sorted; most 

sands are medium to fine grained; pebbly at some 

horizons ....... ..................................................................................... 659 

45. Volcanic breccia and volcanic sandstone; same as unit 4 7 640 

44. Volcanic siltstone (fine keratophyre tuff?), pale-green; 

weathers light brown; sandy; poorly sorted; graded in 

beds 0.2-0.5 m thick...................................................................... 631 

43. Volcanic breccia and volcanic sandstone (keratophyre 

pyroclastic rocks?), grayish-green; weathers pale yellowish brown; graded beds 0.3-5 m thick; poorly sorted; 

largest clasts in breccia 3 em in diameter ........................ .... 622 

42. Spilite; greenish-black; weathers dark yellowish brown; 

porphyritic, phenocrysts 0.5-1.5 mm in diameter.............. 587 

41. volcanic breccia (keratophyre tuff-breccia?), pale-green; 

weathers light brown; poorly sorted; faint grading; 

volcaniclastic rock fragments dominant .............................. 575 

40. volcanic siltstone, volcanic sandstone, and volcanic breccia, dark-greenish-gray; weathers moderate brown; spilitic composition; graded beds 0.7-3.5 m thick; spilite 

breccia 10m above base ............................................................ 569 

39. Quartz keratophyre, grayish-olive; weathers pale yellowish 

brown; porphyritic, phenocrysts of albite and quartz 

0.2-0.5 mm in diameter; cliff former ...................................... 549 

38. Volcanic sandstone (keratophyre tuff?), grayish-green; 

weathers pale brown; graded beds 0.3-1.0 m thick; poorly 

sorted; feldspar, quartz, and keratophyre rock fragments 

in a chloritic partly silicified matrix; angular fragments 532 

37. Volcanic breccia (spilite tuff-breccia?), greenish-black; 

weathers dark yellowish brown;· spilitic composition; 

grades to sandstone (tuff) in beds 1.0-2.5 m thick; poorly 

sorted; calcareous; chloritic matrix; forms grassy slopes 518 

36. Spilite, greenish-black; weathers dark yellowish brown; 

porphyritic, phenocrysts 0.1-0.3 mm in diameter; may be 

a sill.................................................................................................... 440 

35. Volcanic sandstone and volcanic siltstone (keratophyre 

tuff?), grayish-green; weathers pale brown; graded in 

beds 0.2-0.8 m thick; poorly sorted; feldspar, quartz, and 

rock fragments in a partly silicified matrix........................ 438 

34. Spilite tuff, greenish-black; weathers dark yellowish brown; 

graded beds 0.2-0.8 m thick; weathers to form grassy 

slopes ................................................................................................ 435 
STRATIGRAPHY 21 

Reference section, Hunsaker Creek Formation-Continued 

Unit Description Cumulative thickness 

33. Volcanic sandstone (keratophyre tuff?), pale-green; weathers light brown; graded from coarse to fine sand; crystal 

above base of section 

(m) 

rich with albite dominant-·--------------------------------·------·--------------- 430 

32. Volcanic sandstone and volcanic siltstone, pale-green and 

dusky-red; weathers in shades of brown; graded in beds 

0.2-0.4 m thick; poorly sorted---------------------·------- --------------·------- 418 

31. Volcanic breccia (keratophyre tuffbreccia?), grayish-green; 

weathers pale brown; graded; poorly sorted_--------------·------- 413 

30. Volcanic sandstone, grayish-green; weathers pale yellowish brown; graded in beds 0.2-0.8 m thick; coarse to 

medium sand sizes; poorlly sorted; some grains are 

rounded -----------------------------------·---------------------------------··--------------·------- 409 

29. Volcanic sandstone, dusky-red; weathers light brown; 

medium grained; poorly sm·ted -------------------------·-------------- _______ 396 

28. spilite tuff, greenish-black; weathers dark yellowish 

brown; fine grained, graded beds 0.2-1.0 m thick_____________ 395 

27. Volcanic breccia and volcanic sandstone (keratophyre tuffbreccia and tuff?), grayish-green; weathers light brown; 

graded beds 0.3-2.0 m thick; angular clasts; poorly 

sorted ---------------------------------------- __________________________________ ·- __________ --· _ ______ 392 

26. Volcanic siltstone (keratophyre tuff?), grayish-green, 

weathers light brown; poorly sorted; sandy; fine grading 

in beds 0.1-0.3 m thick--------------------------------------------------------·------- 380 

25. Volcanic sandstone, volcanic siltstone, and volcanic breccia (keratophyre tuff and tuff-breccia?), pale-green; 

weathers light brown; graded beds 1.0-2.5 m thick; 

poorly sorted; banded on w1eathered outcrops ------------·------- 377 

24. Volcanic siltstone, very dusky red; weathers dark yellowish 

brown; fine grained; beds 0.2-0.4 m thick; faint grading 353 

23. Volcanic sandstone and voleanic siltstone (keratophyre 

tuff?), pale-green; weathers pale brown; graded in beds 

0.3-3.0 m thick; poorly sorted; angular fragments; finer 

grained beds are laminated; cliff former -----------------------·------ 349 

22. Spilite, greenish-black; weathers dark yellowish brown; 

porphyritic; phenocrysts 0.~!-0.5 mm; may be intrusive__ 330 

21. Volcanic siltstone (keratophYJ·e tuff?), pale-green; weathers 

pale brown; fine grained; faint grading------------------------- ______ 329 

20. Volcanic siltstone and volcanic sandstone (keratophyre 

tuff?), pale-green; weathers light brown; graded beds 0.3-

2.5 m thick; poorly sorted; angular grains -------------------·------ 326 

19. Volcanic sandstone and voleanic siltstone (keratophyre 

tuff?), pale-green; weatherB light brown; graded beds 

2-30 em thick; poorly sorted; penecontemporaneous de{ormation structures common; banded appearance in 

outcrop --------------------------------------·------------------------------------------------·------ 309 

18. Spilite, blackish-green; weathers dark yellowish brown; 

vesicular; cliff former; flowB 3-5 m thick·----------------------------- 297 
22 SEVEN DEVILS GROUP, IDAHO AND OREGON 

Reference section, Hunsaker Creek Formation-Continued 

Unit Description Cumulative thickness 

17. Quartz keratophyre flows and tuffs, grayish-green; weathers light brown; flow rocks 1.5-3 m thick and interlayered 

with crystal tuff of same composition; tuff beds are 

above base of section 

(m) 

graded in beds 0.2-1.5 m thick.................................................. 283 

16. Volcanic siltstone (keratophyre tuff?), greenish-gray, 

weathers light brown; pebbly; abundant matrix; weakly 

graded in thin beds ...................................................................... 252 

15. Volcanic sandstone and volcanic siltstone (keratophyre 

tuff?), pale-green; weathers light brown; graded beds 0.7-

3.5 m thick; poorly sorted; angular fragments; banding 

common in finer grained beds; siltstone is silicified ........ 250 

14. Spillite tuff-breccia, brownish-black; weathers dusky 

yellowish brown; clasts 0.5-5.0 em; graded beds 0. 7-4.5 

m thick .............................................................................................. 232 

13. Volcanic sandstone, volcanic siltstone, and volcanic breccia (keratophyre tuff and tuff-breccia?), pale-green; 

weathers light brown; graded beds 0.3-3.0 m thick; 

poorly sorted; large (5 mm) quartz and albite crystals in 

pale green; partly silicified matrix.......................................... 183 

12. Spilite, greenish-black; weathers dark yellowish brown; 

porphyritic, phenocrysts 0.2-2.5 mm in diameter; amygdaloidal ............................................................................................ 131 

11. Volcanic siltstone, volcanic sandstone, and volcanic breccia (keratophyre tuff and tuff-breccia?), pale-green; 

weathers light brown; graded beds 1.0-4.5 m thick; 

angular to subangular grains .. :............................................... 124 

10. Volcanic siltstone, grayish-purple; weathers dark yellowish 

brown; pebbly; poorly sorted; pebbles subrounded ............ 69 

9. Spilite tuff-breccia, greenish-black; weathers dark yellowish brown; clasts 2.0-4.0 em; weakly graded in beds 

1.0-2.5 m thick................................................................................ 68 

8. Spilite, greenish-black; weathers dark yellowish brown; 

porphyritic; phenocrysts 0.3-1.0 mm in diameter.............. 65 

7. Volcanic sandstone and volcanic siltstone (keratophyre 

tuff?), grayish-green; weathers light brown; graded beds 

0.3-2.5 m thick; poorly sorted; angular fragments; some 

breccia ································-·-··························································· 64 

6. Volcanic siltstone, grayish-green; weathers light brown; 

poorly sorted; graded; pebbly; pebbles up to 1.0 em in 

diameter and subrounded .......................................................... 52 

5. Spilite tuff, dark-greenish-gray; weathers dark yellowish 

brown; graded beds 0.2-2.5 m thick; poorly sorted; feldspar phenocrysts and microlites scattered irregularly 

in a chloritic matrix ............................. .'...................................... 51 

4. Volcanic sandstone (keratophyre tuff?), grayish-green and 

moderate-red; weathers to light brown and dark yellowish brown; graded beds 0.2-3.0 m thick; poorly 

sorted ·························································-··························-··········· 37 
STRATIGRAPHY 23 

Reference section, Hunsaker Creek Formation--Continued 

Unit Description Cumulative thickness 

above base of section (m) 

3. Spilite, dark-greenish-gray; weathers yellowish brown; 

porphyritic; amygdaloidal.......................................................... 10 

2. Volcanic siltstone and volcanic sandstone (keratophyre 

tuff?), grayish-green; weathers pale brown; graded; some 

load casts apparent ·----·-···--·------·---------------·-·---------------·--------· ·------ 5 

1. Spilite tuff, dark-maroonish-black; weathers dark yeliowish brown; coarse grained; poorly sorted; spilite J~ock 

fragments and feldspar crystals set in a maroonish-bl ack 

matrix -----------------------------------·---·----·-----------·--------·-·--·-----·----·------- ....... 2 

Base of section is near the bed ofBal1ard Creek about lOOm we!st of the Idaho Power 

and Light Company powerline road. This is not the base of the formation. 

Total thickness of the reference section is 676 m. 

The formation is distinguished from the underlying Windy 

Ridge Formation by the presence of abundant conglomerate, 

volcanic sandstone, keratophyric water-laid tuff, mafic breccia, 

and spilite flows. In most outcrops the formation is difficult to 

distinguish from the overlying Wild Sheep Creek Formation, the 

lower part of which is predominantly volcaniclastic rocks of 

keratophyric (andesitic) cornposition. Th€! probable base of the 

formation is exposed on Windy Ridge in the Blue Creek drainage 

basin, and the top is poorly exposed in the Homestead Creek 

drainage basin (Vallier, 1967; Brooks and Vallier,, 1967) and in the 

southeastern Wallowa Mountains near Fish Lake (Wetherell, 

1960). The upper contact, believed to be an unconformity, is 

generally difficult to map because of similarities of rock type and 

structural complications. Angularity of strata across the 

unconformity cannot be established in either area, although that 

possibility should not be discarded because the evidence is 

inconclusive. 

The total thickness of the Hunsaker Creek Formation is not 

known. The sections at Hunsaker and Ballard Creeks probably are 

not equivalent, and together they total nearly 1,500 m. An estimate 

of 2,500 m seems valid, although it may be conservative. In the 

southeastern Wallowa Mountains, if there is no significant repetition due to faulting, the thickness may be as mwch as 3,500 m. 

Rocks are mostly volcanogenic, consisting of pyroclastic breccia, agglomerate, tuff, epiclastic volcanic breccia, conglomerate, 

sandstone, siltstone, and minor limestone with quartz keratophyre 

and spilite flow rocks. The flow rocks form only a small part of the 

formation, but small hypabyssal plutons of quartz keratophyre 

and metamorphosed mafic roeks are common. Most volcaniclastic 
24 SEVEN DEVILS GROUP, IDAHO AND OREGON 

beds are vertically graded, and some sequences of graded beds are 

more than 150 m thick in the Hunsaker Creek area. Many of these 

clastic beds are feldspathic tuffs, whereas others contain a large 

diversity of clast types from several different source areas. 

Volcanic flow rocks are mostly spilite and quartz keratophyre. 

Quartz keratophyre flow rocks occur in scattered discontinuous 

outcrops and range in thickness from 3 to 20m. Small hypabyssal 

plutons of the same composition are common. All quartz 

keratophyre specimens examined in thin section are porphyritic, 

consisting of albite and quartz phenocrysts set in a felty, 

trachytic, or completely recrystallized groundmass. Quartz 

phenocrysts range in shape from bipyramidal to rounded, 

depending on the amount of resorption. 

Mafic minerals are generally absent from the quartz keratophyre; chlorite replaces some small amphibole grains. Major 

groundmass minerals are quartz, albite, chlorite, calcite, sphene, 

white mica, and hematite. Minor amounts of epidote and prehnite 

occur along some thin veins. Mineralogies show a near equilibrium 

in the greenschist facies, with albite the only plagioclase present. 

The rocks have undergone variable recrystallization and silicasodium metasomatism. Recrystallized quartzose groundmasses, 

which often contain quartz spherulites, probably are the result of 

glass devitrification and later metamorphism. Low values of 

potassium and calcium combined with a high sodium content 

(table 3) indicate significant amounts of large ion mobility, 

although the time and amount of mobilization are not known. 

Spilite occurs as flows and irregular hypabyssal intrusions. 

Flows are generally no thicker than 5 m. Most specimens are 

porphyritic, with phenocrysts of plagioclase and clinopyroxene (or 

chlorite pseudomorphs of clinopyroxene) set in groundmasses 

having intergranular, diabasic, and pilotaxitic textures. Major 

oxide composition of two spilites are given in table 3, and modal 

analyses of three representative spilite specimens are given in 

table 4. The original basalts probably were low-potassium 

tholeiites. 

Pyroclastic rocks include keratophyre and spilite tuff-breccia, 

agglomerate, and coarse- and fine-grained tuff. Individual units, 

generally comprising several beds, reach thicknesses of 50-100m. 

Crystal tuff beds in the type section of the Hunsaker Creek 

Formation are graded, with plagioclase crystals up to 5 mm in 

length in a chlorite matrix. Clasts in spilitic breccias, some more 

than 1m in diameter, are set in a dark-green chlorite matrix._ 

True epiclastic beds, particularly those of smaller grain sizes, are 

difficult to distinguish from tuff. However, a large part of the 
STRATIGRAPHY 25 

TABLE 3.-Quartz keratophyre and spilite chemistries from the Hunsaker Creek 

Formation 

[Analyses by U.S. Geological Survey laboratory (Shapiro and Brannock, 1962)] 

Oxide VC-15 

(Quartz keratophyre) 

Si02 ..... ·--·-·---·-·-·--···---·-·-·-·-··· 78.70 

Ti02 ·---·-----·-·-·-·--·-·-·---···-·-··--· .24 

Al203 ·-·--·-·-··--------···-·-·-··-·-·--- 11.90 

Fe203 ·-·--·-··---··-·-·····-·-···--·-·- 1.00 

FeO ·-·---·----·-·-·--··-·-·-·-···-··-·-···- .16 

MnO ·-·--·-·-···-·---·-··--·-·-····-·-···- .04 

MgO --·----·---·-·-···-·-···-······-·····- .24 

CaO -·---·-·-···---···-·-·-·-··-···-·---·- .00 

Na20 ·----·-·-···---·-·-···-··--··-·-·-·- r).80 

K20 -·---·-·-·-·-·-·-·-·--·-·-····--·----· .15 

P205 -·-·-···-·-·-·-·--·-·-·-·-·-·-----·· .08 

H2o+-·-·····-··--·-·-··-·-·-·····-···-·--- .57 

H20----·-·-··----·-···-··-----·-·---·----· .15 

C02 -·-·-·-·--·-·--··-·-·-·-·-·-·-··-····· .06 

Total --·-·-·-·-·-·-··-···-·--·· 9H.09 

VC-131 

(spilite) 

[)1.90 

1.80 

15.90 

4.30 

5.10 

.20 

3.30 

9.60 

3.00 

.02 

.35 

3.10 

.36 

.05 

H8.98 

VC-197 

(spilite) 

51.40 

.88 

16.40 

2.80 

5.00 

.16 

7.40 

6.00 

4.00 

.08 

.20 

4.10 

.79 

.08 

99.29 

TABLE 4.-Modal analyses of three spilites, Hunsaker Creek Formation 

(Tr., trace] 

Mineral LS9-3 LS9-4 VC-197 

Plagioclase ··-··-··-·-·-·-···--·-·-·- 70.1 73.1 50.6 

Augite ···-----·-·-------·--·-·-····-···- ············-··--·-·· -·------------------ 5.9 

Opaque minerals ------------·- .2 1.1 .2 

Chlorite --------·----------------·----·- ~n.1 25.1 36.5 

Calcite ---·----------·-·--·-·-----··----- 4.4 .1 Tr. 

Sphene---------·---···---·------------·- .6 Tr. 6.8 

Leucoxene -·----··---·-------··----- .6 .3 Tr. 

Quartz -·-·-·-------·-------·----··------ 3.0 .3 Tr. 

White mica-·-·-·-------·------------ ·-·------·---------- -------------------- Tr. 

Epidote -----··----·---·-·----···------- ·--------·---------- -------·------------ Tr. --------------- -------------------- Total -·-·-·-·--------·-·---·--- 100.0 100.0 100.0 

clastic rocks, estimated to be at least 50 pe:rcentoftheformation, is 

epiclastic conglomerate, breccia, sandstone, and siltstone. 

Dominant components in the coarser grained beds are clasts of 

quartz keratophyre and spilite. In finer grained beds, crystals of 

albite, quartz, and lithic n~agments are set in a green chlorite 

matrix. Sandstone mostly is volcanic graywacke (modal analyses 

of representative volcanic graywackes are given in table 5). 

Volcanic siltstone makes up a large perc:entage of the epiclastic 

rocks. Studies of 41 thin sections show that the siltstone has 

components with the following ranges: matrix of chlorite, clay, 

fine-grained fragments, and very fine grained quartz and feldspar 

(70-80 percent); plagioclase grains (10-15 percent); quartz (3-5 
26 SEVEN DEVILS GROUP, IDAHO AND OREGON 

TABLE 5.-Modal analyses of volcanic graywacke, Hunsaker Creek Formation, 

in volume percent 

[1,000 points counted. Tr., trace] 

Mineral LS7-23 T-1-1-12 VC-286 

Plagioclase -------------------------- 21.1 29.2 68.4 

Quartz ---------------------------------- 30.8 18.8 14.8 

Rock fragments ---------------- 4.6 3.2 1.6 

Quartz/albite matrix ------ 40.5 45.5 4.4 

Iron ore -------------------------------- 1.9 .5 .9 

Chlorite -------------------------------- .3 .5 9.1 

Calcite ---------------------------------- .5 1.7 .3 

Sphene/leucoxene ------------ .3 .8 .5 

White mica -------------------------- Tr. . 8 Tr . Epidote -------------------------------- Tr. Tr. Tr. 

Totals ------------------------ 100.0 100.0 100.0 

percent); and rock fragments (1-3 percent). Minor constituents are 

calcite, sphene, leucoxene, white mica, epidote, and prehnite. 

Conglomerate makes up to least 10 percent of the formation. All 

gradations exist between pebbly mudstone and well-sorted 

conglomerate with clasts of cobble and boulder sizes. Some beds 

are more than 20 m thick and have clasts up to 30 em in diameter. 

Pebble counts at six conglomerate outcrops indicate the following 

clast proportions: quartz keratophyre (50 percent); volcaniclastic 

rocks (35 percent); spilite (8 percent); and unknowns (7 percent). 

Rare clasts of quartz diorite and quartz-bearing gabbro also occur. 

Current measurements in epiclastic rocks show that many 

currents were from the southwest and west. Coarse breccia and 

conglomerate are slightly more abundant in the western part of the 

mapped area, suggesting a western source. Volcanism was 

contemporaneous with tectonism, erosion, and deposition; many 

of the tuff beds probably are the result of subaqueous pyroclastic 

flows. Clasts of gabbro and quartz diorite in conglomerates · 

indicate deep erosion of the source terrane. 

The Hunsaker Creek Formation is of Early Permian age. F. G. 

Stehli (written commun., 1965) reported that brachiopod faunas 

are of Leonardian or Guadal upian age and most likely are of Word 

(Guadalupian) age. Some of the Clover Creek Greenstone in the 

Wallowa Mountains is of Permian and Triassic age; the Permian 

rocks probably are equivalent to parts of the Hunsaker Creek 

Formation. 

The Hunsaker Creek Formation records an important step in the 

evolution of a volcanic arc in the Pacific Ocean during the Early 

Permian Epoch. Andesitic and dacitic volcanism indicates 

extensive silicic volcanism and strongly suggests that subduction 

was occurring along the arc. The exposed Permian rocks are only a 

small remnant of a previous large and extensive island arc 
STRATIGRAPHY 27 

complex, most of which has been subduct«:~d and incorporated into 

the present continental crust. Limestone lenses and pods in the 

Elkhorn Ridge Argillite are in part correlative with rocks of the 

Hunsaker Creek Formation. No paleogeographic reconstruction is 

attempted in this report, however, because the limestone bodies 

probably are allochthonous and may hE~ floating in chert and 

argillite of much younger age (Jones and others, 1976). There is a 

distinct possibility that the Elkhorn Ridge Argillite and Hunsaker 

Creek Formation were deposited on differe~nt plates which are now 

juxtaposed. 

WILD SHEEP CREEK FORMATION 

The Wild Sheep Creek Formation is here named for a thick 

metamorphosed unit of basalt, basaltic andesite and andesite (now 

mostly spilite and keratophyre) flows and volcaniclastic rocks, 

graywacke, argillite, and limestone that is widely exposed in the 

Snake River Canyon and the Seven Devils Mountains. Excellent 

exposures occur along a large part of the canyon, particularly near 

Wild Sheep, Bull, Saddle, and Cherry Creeks. 

The best exposures are in Bull and Saddle Creeks. The type 

section (fig. 6) is designated as the spur between Saddle and Hat 

Creeks, starting near the Snake River frmn 425 to 900 m elevation 

(1,400-3,000 ft), where about 830 m of strata are well exposed. The 

names Saddle Creek and Bull Creek have been used for other rockstratigraphic units in the United States, so the name Wild Sheep 

Creek Formation was chosen because \Vild Sheep Creek is the 

nearest geographic feature of note to the type section and because 

the exposures also are good along it. However, the type section was 

chosen near Saddle Creek because of good exposure and ease of 

access. Wild Sheep and Bull Creeks can be reached only by boat 

from Hells Canyon Dam, whereas Saddle Creek is accessible by 

boat from the lower parts of the Snake River and by trail from the 

road that leads to Hat Point from Imnaha, Oreg. A reference 

section (fig. 7) was chosen from an area farther north, along 

Cherry Creek, where about 440 m of strata were described. 

Type section, Wild Sheep Creek .Formation 

Location: He-Devil 15-minute quadrangle, unsurveyed part of the Snake River Canyon, Oreg. Spur north of 

the mouth of Saddle Creek, across Snake River from the NE% sec. :lO, T. 24 N., R. 2 W., in Idaho. Section is 

between 425 and 900 m elevation (1,400-3,000 ft). Tape and Brunton method used. Rocks are metamorphosed 

to the greenschist facies. Assisted by David Fredley. Top of ridge, grassy slope; not top of formation. 

Unit Description 

21. Diabase, grayish-black; weathers pale brown; coarse 

Cumulative thickness 

above base of section 

(m) 

grained; may be a sill··················---------------·-------·---·---------·----·-------·-··-·····-- 830 
28 SEVEN DEVILS GROUP, IDAHO AND OREGON 

R.2W 

0 1 MILES 

t I 

0 2 KILOMETERS 

T. 

24 

N. 

FIGURE 6.-Type section of the Wild Sheep Creek Formation. Base from U.S. Geological Survey He-Devil 15-minute quadrangle, 1:62,500, 1957. 

Type section, Wild Sheep Creek Formation-Continued 

Unit Description 

20. Basalt breccia, greenish-black; weathers dark yellowish 

brown; clasts 1-2 em in diameter in a chlorite matrix; 

Cumulative thickness 

above base of section 

(m) 

poorly sorted; bedding is indistinct ...................................................... 822 

19. Volcanic breccia, pale-green; pale-green, gray, and lightgray clasts; weak grading to sand sizes in beds 0.3-4.5 m 

thick; some quartz in matrix; clasts angular to subrounded; rare volcanic sandstone beds about 0.2 m thick .............. 810 

18. Diabase; see unit 21 for description .......................................................... 792 

17. Volcanic breccia; see unit 19 for description ················-············-·····-···· 786 

16. Diabase; see unit 21 for description·······················-·····-·-······················-··· 759 

15. Volcanic breccia and volcanic sandstone, light-green; 

weathers to pale brown; clast sizes up to 10 em but average 

1-2 em; graded units 5 m thick near base and 0.5-1.0 m 

thick near top; clasts angular to subrounded; clasts 
STRATIGRAPHY 29 

116° 52' 30" 

45o~~~~~~~~~~~~~~~~~mm~~~~ 

52' 3d, L/ /",0' // /---.... 

0 .5 MILES 

0 1 Kl LOMETERS 

FIGURE 7.-Reference section of the Wild Sheep Formation. Base from U.S. 

Geological Survey Deadhorse Ridge 71/2-minute quadrangle, 1:24,000, 1963. 

Unit 

Type section, Wild Sheep Creek Formation-Continued 

Description Cumulative thickness 

above base of section 

(m) 

15. Volcanic breccia, etc.-Continued 

mostly volcanic flow rocks with some volcaniclastic 

rocks; much less quartz than in unit 19 but still noticeable in hand specimens ----------------------------------------------------------------------------747 

14. Limestone, dark-gray; weathers very pale brown; argillaceous; thin bedded ------------------------------------------------------------------------------------699 
30 

Unit 

SEVEN DEVILS GROUP, IDAHO AND OREGON 

Type section, Wild Sheep Creek Formation-Continued 

Description Cumulative thickness 

above base of section 

(m) 

13. Volcanic sandstone and volcanic siltstone, grayish-green; 

weathers pale brown; graded beds 0.2-4.0 m thick; rare 

breccias at base of thicker graded beds; siltstones are 

darker colored and partly silicified; sandstones have 

abundant feldspar and quartz with some rock fragments -------------------------------------------------------------------------------------------------------------- 697 

12. Volcanic breccia, volcanic sandstone, and volcanic siltstone in graded beds from 0.1 to 7 m thick; breccias 

massive in lower parts with clasts up to 5 em in diameter; 

sandstones are grayish green with white feldspar and 

gray quartz crystals up to 0.5 em in diameter; quartzose 

volcanic arkoses; siltstones are silicified with rare rip-up 

clasts of sandstone in some thin beds ------------------------------------------------ 646 

11. Basalt, dark-greenish-black; weathers to dark yellowish 

brown; porphyritic with phenocrysts up to 0. 7 em in 

length; some thin flow breccia units; flow banding common in porphyritic units; individual flows 10-20 m 

thick ----------------------------------------------------------------------------------------------------------------588 

10. Basalt-breccia, green and grayish-red; weathers yellowish 

brown; some grading---------------------------------------------------------------------------------- 493 

9. Basalt pillow breccia, greenish-black; weathers dark yellowish brown; clasts, many of them fragments of pillows, 

are 2-75 em in diameter; bedding is indistinct -------------------------------- 488 

8. Basalt, dark-greenish-black; weathers yellowish brown; 

series of thin flows 0.5-3 m thick; fine to medium grained; 

rare amygdules --------------------------------------------------------------------------------------------467 

7. Basalt pillow breccia, dark-greenish-black; weathers dark 

yellowish brown; monolithologic; clasts 0.1-0.5 m in 

diameter; indistinct bedding; basalt flows and dikes(?) up 

to 1 m thick cut the sequence; pillow rinds and some 

nearly complete pillows are common; matrix is composed 

of small basalt fragments and chlorite ---------------------------------------------- 44 7 

6. Basalt, dark-greenish-black; weathers dark yellowish 

brown; medium grained; highly fractured; flows 2-3 m 

thick ----------------------------------------------------------------------------------------------------------------127 

5. Covered area; probably fine-grained volcaniclastic rock __________________ 114 

4. Basalt; same as unit 6 ---------------------------------------------------------------------------------- 98 

3. Basalt pillow breccia; same as unit 7 ------------------------------------------------------ 80 

2. Covered area; probably fine-grained volcaniclastic rock------------------ 53 

1. Basalt pillow breccia; same as unit 7; flows, 1-4m thick, 

are more abundant than in other units ---------------------------------------------- 45 

Base of the formation is not exposed; total thickness of the measured type section 

is 830 m. 
STRATIGRAPHY 31 

Reference section, Wild Sheep Creek Formation 

Location: Deadhorse Ridge 7lf:~.-minute quadrangle, unsurveyed part ofthe Snake River Canyon area in eastern 

Oregon, near the north edge of the quadrangle. Section was measured along north side of an unnamed creek 

about 1 km north of Experiment Creek, an east-draining tributary of Cherry Creek. Section described 

beginning near the creek bed of Cherry Creek, elevation from 580 to 855 m (1,900-2,800 ft). Tape and Brunton 

method used. Rocks are metamorphosed to the greenschist facies. Assisted by David Fredley and Larry 

Klueh. Top is grassy slope, not top of section. 

Unit Description 

23. Breccia, dark-green; weathers moderate brown; clasts 1-10 

em in diameter; clast compositions are siltstone, argillite, 

Cumulative thickness 

above base of section 

(m) 

and basalt; beds graded, 1-2m thick ·········-------------------------------------------······----440 

22. Siltstone, argillite, and sandstone, light-green; weathers 

pale brown; graded beds 0.3-40 em thick alternating with 

argillite beds ______________________________________________________________________________________________________________ 426 

21. Basalt, dark-greenish-black; weathers yellowish brown; 

medium grained; porphyritic, with phenocrysts up to 

3 mm in length; individual flows 3-15m thick ___________________________________________ .417 

20. Basalt, dark-greenish-black; weathers yellowish brown; 

medium grained; porphyritic, with phenocrysts up to 

3 em in length; thick flows ----------------------------------------------------------------------------------341 

19. Basalt, greenish-black; weathers dark yellowish brown; 

fine grained; nonporphyritic; individual flows 2-8 m 

thick ----------------------------------------------------------------------------------------------------------------------------317 

18. Basalt; same as unit 21 --------------------------------------------------------------------------------------------301 

17. Basalt; same as unit 20 --------------------------------------------------------------------------------------------296 

Section cut by diorite sill, about 5 m thick. 

16. Basalt; same as unit 21 --------------------------------------------------------------------------------------------283 

15. Basalt; same as unit 20 ------------·------------------------------------------------------------------------------- 239 

14. Basalt, dark-greenish-gray; weathers yellowish brown; 

porphyritic, with phenocrysts up to 5 mm in length; 

one flow unit ___________________________________________________________________________________________ ----------------- 236 

13. Basalt breccia, greenish-gray; weathers yellowish brown; 

clasts up to 3 em in diameter; faint bedding; chlorite 

matrix; weathers to grassy slope --------------------- ------------------------------------------------230 

12. Basalt; same as unit 21 ------------------------------------------- ------------------------------------------------224 

11. Covered area; probably fine-grained volcaniclastic rocks ____________________________ 181 

10. Siltstone and argillite, black; weathers dark brown; thin 

beds 1-40 em thick; faint grading in one bed ________________________________________________ 176 

9. Covered area; probably same as unit 12 -----------·------------------------------------------------170 

8. Basalt, dark-greenish-black, weathers yellowish brown; 

flows 2-4.5 m thick; porphyritic, with feldspar phenocrysts 2-4 mm in length; highly fractured ----------------------------------------------------165 

7. Limestone, siltstone, and argillite; beds 1-30 em thick; some 

grading; fossil fragments; limestone is dark gray and 

argillaceous; siltstone is calcareous; some grading in 

thicker siltstone beds; weathers to gentle grassy slope ____________________________ 152 
32 SEVEN DEVILS GROUP, IDAHO AND OREGON 

Reference section, Wild Sheep Creek Formation-Continued 

Unit Description 

6. Basalt, dark-greenish-black; weathers to yellowish brown; 

flows 2-5 m thick; fine grained; some flows are porphyritic with phenocrysts 2-8 mm in length; fractured 

Cumulative thickness 

above base of section 

(m) 

rocks ----------------------------------------------------------------------------------------------------------------------------126 

5. Covered area; probably a basalt breccia ------------------------------------------------------------ 81 

4. Basalt; same as unit 6 ---------------------------------------------------------------------------------------------- 77 

3. Covered area; fragments of limestone and argillite; probably a limestone, siltstone, and argillite unit similar 

to unit 7 ---------------------------------------------------------------------------------------------------------------------- 45 

2. Basalt; same as unit 6 ·-·-···-------------------·----·-·-----·--·-·-·---·-----·------·-·--------------------··------ 17 

1. Basalt breccia, dark-greenish-gray; weathers yellowish 

brown; clasts of basalt 3-8 em in diameter in a chlorite 

matrix; weakly bedded -·--·-··-·---------------·-·------------·--------------·---·-·----·-----·----·----·------- 6 

Base of the formation is not exposed; total thickness of the reference section is 

440m. 

Distinguishing characteristics are rugged outcrops, thick flow 

and volcaniclastic units, dark-green and greenish-black colors on 

fresh surfaces, and the metamorphosed basalt, basaltic andesite, 

and andesite compositions of the flows and coarse volcaniclastic 

beds. Argillite and graywacke form units more than 100 m thick 

that increase in relative abundance toward the north; excellent 

exposures are found near the mouth of the Salmon River. Limestone units also are more abundant and thicker in the northern 

part of the area and are especially well exposed between the 

mouths of the Salmon and Grande Ronde Rivers. 

The Wild Sheep Creek Formation unconformably overlies the 

Hunsaker Creek Formation in the southern part of the Snake River 

Canyon. In the Wallowa Mountains, lithologically correlative 

rocks are assigned to the Clover Creek Greenstone. In the Sparta 

region, south of the Wallow a Mountains, correlative rocks overlie 

gabbro and quartz diorite (Prostka, 1963). 

The formation is conformably overlain by the Doyle Creek 

Formation and unconformably by the Coon Hollow Formation 

near Jim Creek in the northern part of the Snake River Canyon. 

Where the maroon Doyle Creek Formation overlies the Wild Sheep 

Creek Formation along the walls of the Snake River Canyon, there 

is a gradation from dark-green and greenish-black flows and 

volcaniclastic rocks to maroon volcaniclastic and flow rocks, with 

conglomerate and other epiclastic rocks becoming more abundant 

with stratigraphic elevation. Because of rapid lithofacies changes 

over short distances, structural deformation, and a lack of good 
STRATIGRAPHY 33 

fossil control, criteria were not available in all areas to distinguish 

the formations; therefore, the boundaries will need further 

refinement after additional studies. Probably the best distinguishing characteristic is the abundance of maroon epiclastic 

debris in the Doyle Creek Formation; the base of the Doyle Creek 

Formation may best be placed at the bottom of the lowermost 

conglomerate or epiclastic sandstone bed in the maroon-colored 

unit. In the Pittsburg Landing area the contact between the Wild 

Sheep Creek and Doyle Creek Formations is poorly defined. In 

general, it was drawn where dominantly brown epiclastic debris 

overlies greenish-black volcanic flows and thick coarse-grained 

volcaniclastic units. 

In general, three units can be distinguished in the Wild Sheep 

Creek Formation. The lower part is mostly volcaniclastic, with 

keratophyric (andesitic) compositions dominant. Good exposures 

are along the ridge north of Homestead Creek and near the mouth 

of Salmon River, where argillite and sandstone sequences are 

exposed. The thick middle unit is mostly spilitic (basaltic) in 

composition with massive and pillowed flows, thick beds of coarse 

breccia, and mafic tuff beds dominant. Good exposures of this unit 

are near Hells Canyon Dam, at Saddle Creek, and along the river 

near the mouth of Jones Creek. The upper unit is mostly a mixture 

of spilitic and keratophyric clastic rocks, argillite, and limestone. 

Sandstone beds are notably quartz rich. Good exposures are near 

the top of the section in the Bull, Cache, and Saddle Creek areas 

and in the Cherry and Cook Creek areas. These units are not easily 

distinguished in the southern part of the area between Ashby 

Creek and Lynch Creek because of abundant lithofacies changes 

and structure. 

Maximum thickness of the Wild Sheep Creek Formation is 

estimated to be 2,500 m. Thickest individual sections are near the 

type area and in the Seven Devils Mountains. The formation seems 

to thin both to the north and south, although this might be due to 

structurally related differential erosion. 

Major lithologies are massive lava flows, pillow lavas, flow and 

pillow breccia, and volcaniclastic rocks. Most are of metamorphosed basalt, basaltic andesite, and andesite (spilite and 

keratophyre) compositions. Epiclastic rocks, including breccia, 

conglomerate, graywacke, and argillite are important contributors, and in places argillaceous limestone makes up a 

significant part of the stratigraphic section. All rocks are 

metamorphosed to the greenschist facies, although most mineral 

assemblages have not reached equilibrium in that facies. 

Basaltic rocks are mostly massive and pillowed flows and flow 
34 SEVEN DEVILS GROUP, IDAHO AND OREGON 

and pyroclastic breccia. Some flows reach thicknesses of 20 m, 

whereas local accumulations of breccia are as thick as 100 m. 

Primary textures in flow rocks are dominantly glomerophyric, 

pilotaxitic, and porphyritic intergranular. In some flow rocks, 

phenocrysts are up to 5 em long and glomerols form clusters and 

rosettes 3-7 em in diameter. Dominant minerals are plagioclase, clinopyroxene, iron ore, chlorite, epidote, calcite, quartz, 

prehnite, sphene, leucoxene, and white mica (table 6). Plagioclase 

compositions range from labradorite to albite as determined by 

optics and X-ray diffraction. Common alteration minerals of the 

plagioclase are epidote, chlorite, calcite, and white mica. Fresh 

clinopyroxene (augite) crystals occur in many of the flow rocks, but 

generally they are partly or wholly replaced by chlorite and 

epidote, rarely by actinolite. Chlorite pseudomorphs after olivine 

are evident in a few thin sections. Iron ores are mostly magnetite, 

although titaniferous magnetite and ilmenite, often partially 

replaced by leucoxene, are common. Calcite occurs in veins, as a 

pseudomorph mineral, and as granoblastic growths in finegrained groundmasses. 

The flow rocks show a wide range in major oxides (table 7). Most 

are poor in potassium, and there are wide variations in sodium 

contents. Silica content ranges from about 50 to nearly 60 percent 

for the basic rocks and is greater than 60 percent for keratophyric 

rocks. 

Flow rocks of keratophyric composition are light green and light 

maroon and contain small phenocryst of feldspar in a quartzose 

groundmass. These probably make up no more than five percent of 

the flow rocks. However, there are localities where they are more 

abundant. One of these localities is along the !PALCO (Idaho 

Power and Light Company) road, across from McGraw Creek, 

where both flow and pyroclastic rocks are exposed. 

Epiclastic and pyroclastic rocks, like the volcaniclastic rocks of 

the Hunsaker Creek Formation, are difficult to distinguish. This is 

particularly true of units that have been derived from a monolithologic terrane and have undergone metamorphism. Without 

good criteria such as the presence of pumice and fine ash, lobate 

and cuspate volcanic rock fragments, and glass shards, origins 

generally cannot be distinguished. Volcaniclastic rocks occur in 

bold outcrops all along the IP ALCO road between Limepoint Creek 

and Big Bar. Many of these probably are pyroclastic. Dark-green, 

light-green, and maroon clasts are set in a light-green or lightmaroon matrix. Some beds are graded, whereas others are 

massive. 

Epiclastic rocks are dominant over pyroclastic rocks in the 
STRATIGRAPHY 

TABLE 6.-Modal analyses of representative flow rocks, Wild Sheep Creek 

Formation 

[VC-262 groundmass of quartz and plagioclase; Tr., trace; 1,200 points counted] 

VC-269 VB-87 VB-85 VC-262 

Mineral (quartz 

35 

(spilite) (spilite) (spilite) keratophyre) 

Plagioclase phenocrysts 

Plagioclase microlites .. .. 

Clinopyroxene ................ .. 

Opaque minerals ............. . 

Quartz ................................. . 

Epidote .............................. .. 

Chlorite ............................... . 

White mica ........................ .. 

Prehnite ............................ .. 

Sphene ................................ .. 

Leucoxene ......................... . 

Calcite ................................. . 

Groundmass .................... .. 

Total ........................ .. 

24 

39 

16 

9 

3 

Tr. 

2 

6 

1 

11 

66 

2 

4 

1 

7 

6 

------------------

------------------

------------------

------------------

1 

2 

11 

39 

36 

2 

--------------------

4 

6 

--------------------

--------------------

1 

1 

--------------------

-----·--------------

12 

15 

. ~-.- ----------- -- 2 

1 

Tr. 

3 

------------------

------------------

Tr. 

Tr. 

1 

66 ---------------------------------------- 100 100 100 100 

TABLE 7.-Chemical analyses of representative flow rocks from the Wild Sheep 

C1·eek Formation 

[Analysis by R. Batiza; see table 6 for rock types] 

Oxide VC-269 VB-87 VB-85 VC-262 

Si02 ...................................... 50.60 55.60 48.20 73.60 

Ti02 ...................................... .99 1.20 2.09 .36 

Al203 .................................... 17.50 15.80 15.00 14.10 

FeO(total iron) .................. 9.17 8.59 12.92 2.25 

MnO ...................................... .19 .19 .22 .05 

MgO ...................................... 4.57 3.95 5.87 .01 

CaO ...................................... 8.17 7.82 7.99 .57 

Na20 .................................... 4.74 5.77 4.76 5.99 

K20 ...................................... 1.00 1.15 .20 .82 

P205 .................................... .12 .................. .31 .04 ---------------------------------------- Total .......................... 97.05 100.07 97.56 97.79 

formation. Most are conglomerate, breccia, graywacke, siltstone, 

and argillite. Conglomerate is abundant along Grassy Ridge north 

of Kinney Creek, where beds range in thickness between 1 and 15 

m. Clast sizes reach 15 em; all are well rounded to subrounded and 

are composed of vesicular basalt (spilite). Breccias are the 

dominant volcaniclastic deposits; most are composed of basaltic 

clasts in a chloritic sandy matrix. Clasts in breccias that crop out 

just north of Pittsburg Landing along the Snake River are as long 

as 5 m. Graywacke is an abundant rock type. In the lower parts of 

the formation, graywackes are made up of andesitic rock 

fragments and feldspar in a matrix of chlorite or calcite or both. In 

the upper parts of the formation, however, quartz and feldspar are 
36 SEVEN DEVILS GROUP, IDAHO AND OREGON 

the major components, and many beds are arkosic. Some siltstone 

and argillite beds are silicified, and one thin section from a silicified argillite on Grassy Ridge contains spherical chalcedonic 

structures that probably are recrystallized Radiolaria tests. 

Limestone beds in the Wild Sheep Creek Formation are exposed 

in several parts of the Snake River Canyon and in the southeastern 

Wallowa Mountains. Best exposures are along Bull, Hat, Cherry, 

and Jim Creeks, where argillaceous limestone occurs in units as 

much as 100m thick. Some recrystallized lenses of carbonate as 

much as 0.5 km in length probably mark massive submarine 

slides. These protrude as rugged shoulders along the canyon walls 

and should not be confused with the bedded limestone units. 

The Wild Sheep Creek Formation is latest Middle Triassic 

(Ladinian) on the basis of species of Daonella and early Late 

Triassic (Karnian) on the basis of species of ammonites (age determinations by N.J. Silberling). Correlative rocks include the upper 

part of the Clover Creek Greenstone in the Wallow a Mountains 

and the Upper Triassic volcanic rocks (Brooks and others, 1977) 

that are exposed near Huntington, Oreg. 

DOYLE CREEK FORMATION 

The Doyle Creek Formation is here named for a thick section of 

red and green metamorphosed volcaniclastic rocks and volcanic 

flow rocks that are well exposed in Doyle Creek, the first major 

creek north of Big Bar on the Oregon side of the Snake River (fig. 8). 

Rocks of this formation are discontinuously exposed, mostly along 

the Oregon side of the Snake River, between Ashby and Saddle 

Creeks in the southern part of the area, at Pittsburg Landing in the 

central part, and near Cook Creek in the northern part. It also 

crops out beneath the Martin Bridge Limestone along the Snake 

River south of the Grande Ronde.River mouth. 

The distinguishing characteristics of this formation are the red 

colors and the abundance of epiclastic sediments. The red colors 

contrast sharply with the underlying green Wild Sheep Creek 

Formation, and lithologies differ because of the high epiclastic 

sediment content in the Doyle Creek Formation. Lithofacies 

changes are rapid, and even closely spaced stratigraphic sections 

show wide variations in thicknesses of beds and compositions. 

The type section along Doyle Creek contains more flow rocks 

than the two reference sections (figs. 9, 10), which generally were 

measured in younger strata of the formation and contain more 

volcaniclastic rocks. The base of the formation is not well defined, 

because the green flow rocks and volcaniclastic rocks of the Wild 

Sheep Creek Formation grade into the red dominantly epiclastic 
0 

I 

0 

STRATIGRAPHY 

R.3W. 

1 MILES 

I I 

2 KILOMETERS 

FIGURE 8.-Type section of the Doyle Creek Formation. Base from U.S. 

Geological Survey Cuprum 15-minute quadrangle, 1:62,500, 1957. 

37 

rocks of the Doyle Creek Formation over a vertical distance ofl00-

200 m. The base of the formation is taken as the bottom of the first 

thick red epiclastic volcanic breccia at Doyle Creek. The Doyle 

Creek Formation is most likely conformable on the Wild Sheep 

Creek Formation in the Doyle Creek area; elsewhere definite 

relations were not established, but the contact probably is 

conformable. The formation is overlain, probably unconformably, 

by the Upper Triassic Martin Bridge Limestone. Excellent 

exposures of the upper contact are along the south side of Kinney 

Creek near the IP ALCO road and just south of Eckels Creek, along 

the same road, where the youngest beds are red and green volcanic 

breccia. Another good exposure is along the north side of McGraw 

Creek, where the youngest rock in the Doyle Creek Formation also 

is a thick unit of breccia. 

Formation boundaries were most difficult to map in the area 

between Limepoint Creek and Hibbles Gulch along the Idaho side 

of the Snake River. Here, the base of the Doyle Creek Formation 

was mapped below a sequence where red epiclastic rocks are 

dominant. However, much of the underlying Wild Sheep 
38 SEVEN DEVILS GROUP, IDAHO AND OREGON 

T. ft.'i'l.i:""'/n~~6~·\:l,-)tl 20 

N. 

R.4W. 

0 1 MILES 

I I I 

0 2 Kl LOMETERS 

FIGURE 9.-Reference section of the Doyle Creek Formation along the north side of 

McGraw Creek. Base from U.S. Geological Survey Homestead 15-minute 

quadrangle, 1:62,500, 1957. 

CreekFormation also is made up of volcaniclastic rocks, some of 

them red, and further refinement of the contact is necessary. The 

red color by itself is not a good criterion for distinguishing the two 

formations; rather, the red color should be combined with the 

abundance of epiclastic rocks to separate the Doyle Creek 

Formation from the Wild Sheep Creek Formation. 

Type section, Doyle Creek Formation 

Location: Cuprum 15-minute quadrangle; unsurveyed part of the Snake River Canyon area in Oregon; across 

the river from the center of sec. 17, T. 21 N., R. 3 W. Measured along the north side of the south fork of Doyle 

Creek from an elevation of about 855 m (2,800 ft) to the contact with the Columbia River Basalt Group at 

1,000 m (3,600 ft). Jacobs Staff and tape and Brunton methods used. Rocks are metamorphosed to the greenschist facies. Top is contact with the Columbia River Basalt Group. It is not the youngest part of the 

formation. 

Unit Description 

10. Conglomerate; dusky-red matrix; weathers pale reddish 

brown; interbedded sandstone and some volcanic flow 

rocks; clast sizes 0.2-10 em; volcanic flow rocks are dominant clast types; some clasts of volcaniclastic and pluCumulative thickness 

above base of section 

(m) 
STRATIGRAPHY 

R.48E. R.4W. 

0 1 MILES 

I I 

0 2 Kl LOMETERS 

FIGURE 10.-Reference section of the Doyle Creek Formation along the 

second gully north of Ashby Creek. Base from U.S. Geological Survey 

Homestead 15-minute quadrangle, 1:62,500, 1957. 

Type section, Doyle Creek Formation-Continued 

39 

Unit Description Cumulative thickness 

above base of section 

(m) 

10. Conglomerate, etc.-Continued 

tonic rocks; poorly sorted; many beds graded; some crosslamination in the sandstone beds --------------------------------------------------------301 

9. Basalt, dusky-red; weathers pale reddish brown; porphyritic, with phenocrysts of plagioclase 1 em long in a 

medium-grained groundmass ------------------------------------------------------------------240 

8. Conglomerate; same as unit 10 ------------------------------------------------------------------232 

7. Volcanic breccia (pyroclastic breccia?), dusky-red; weathers 

moderate yellowish brown; graded bedding; poorly 
40 SEVEN DEVILS GROUP, IDAHO AND OREGON 

Type section, Doyle Creek Formation-Continued 

Unit Description 

7. Volcanic breccia, etc.-Continued 

sorted; reddish-brown volcanic flow, volcaniclastic, and 

pumice clasts range from 0.1 to 8.0 em in diameter; 

breccia grades into sandstone and siltstone in beds 1.0-

Cumulative thickness 

above base of section 

(m) 

3.5 m thick ----------------------------------------------------------------------------------------------------216 

6. Basalt, very dusky red; weathers to dusky brown; individual 

flows 1.0-2.5 m thick; most flows are porphyritic, with 

phenocrysts from 0.5 to 2.0 m long; medium-grained 

groundmass --------------------------------------------------------------------------------------------------197 

5. Diorite sill; 12m thick 

4. Basalt; same as unit 6; one flow about 15 m thick; some 

phenocrysts 1 em long ------------------------------------------------------------------------------180 

3. Andesite (keratophyre?), pale-green; weathers dusky yellow; porphyritic, with phenocrysts 0.3-1.0 mm long------------------------ 72 

2. Volcanic breccia, dusky-red; weathers pale reddish brown; 

graded bedding; some interbedded thin basalt flows, 1-

3m thick; poorly sorted; clast diameters 0.1-10 em; clasts 

subangular, some subrounded; most clasts from flow 

rocks; epiclastic rock unit -------------------------------------------------------------------------- 66 

Wild Sheep Creek Formation 

1. Basalt, dusky-red, grayish black, and dark-greenish-gray; 

weathers dark and moderate yellowish brown; thick 

sequence of flows 5-15 m thick; some intercalated volcaniclastic (tuffaceous) units; most flows are porphyritic, 

with phenocrysts from 0.3 to 5.0 mm in length ________________________________ l16 

Doyle Creek Formation is 301 m thick at the type section. It conformably overlies 

flows of the Wild Sheep Creek Formation. 

Reference section, Doyle Creek Formation 

Location: Homestead 15-minute quadrangle; unsurveyed part of the Snake River Canyon in Oregon. Measured 

along the north side of McGraw Creek beginning 50 m above the creek bed, elevation 670 m (2,200 ft) and continuing to the contact with the Martin Bridge Limestone at about 855 m (2,800 ft). The mouth of McGraw 

Creek is across the river from the N1!2 sec. 1, T. 20 N., R. 4 W., in Idaho. Tape and Brunton method was used to 

measure thicknesses. Rocks are metamorphosed to the greenschist facies. Top of section is the basal unit of 

the Martin Bridge Limestone. 

Unit Description 

Martin Bridge Limestone 

6. Siltstone, calcareous, pale-green; weathers to pale brown; 

Cumulative thickness 

above base of section 

(m) 

poorly sorted; angular grains; some cross-laminations ________________ 132 

Doyle Creek Formation 

5. Volcanic breccia, dusky-red; dusky-red, pale-green, and 

greenish-black volcanic flow clasts; weathers dusky 

brown; weakly graded in beds 2-10m thick; largest clasts 

10 em in diameter; angular fragments; dacite sill cuts unit 

above 35 m above base -----------------------------------------------------------------------·------128 
STRATIGRAPHY 41 

Reference section, Doyle Creek Formation-Continued 

Unit Description Cumulative thickness 

above base of section 

(m) 

4. Basalt, dusky-red; weathers dusky brown; porphyritic, 

phenocrysts 0.5-1.0 mm in length; medium-grained 

groundmass ----------------------------------------------------------------------------------------------- 52 

3. Volcanic breccia; same as unit 5 with three interlayered 

basalt flows -------------------------------------------------------------------------------------------------- 49 

2. Basalt, dusky-red; weathers dusky brown; porphyritic, 

phenocrysts 1.0-2.0 mm in length --------------------------------------------------- 39 

1. Basalt and volcanic breccia, dusky-red and pale-green; 

weathers dusky brown; breccia beds 1-3m in thickness 

are weakly graded with clasts up to 5 em in diameter__________________ 35 

Base of this section is not the base of the formation. 

Measured thickness is 132 m. 

Reference section, Doyle Creek Formation 

Location: Homestead 15-minute quadrangle; SW1t4NE1!, sec. 2, T. 6 S., R --18 E.; measured along the second 

gully north of Ashby Creek between the elevations of945m (3,100ft) and 1,130m (3,700ft). Tape and Brunton 

method used. Rocks are metamorphosed to the greenschist facies. Top of section is not the top of the formation. Uppermost unit is a grassy slope about 50 m below the contact between the Doyle Creek Formation and 

the Columbia River Basalt Group. 

Unit Description 

10. Conglomerate, dusky-red and grayish-red; weathers pale 

reddish brown; graded beds 1.5-6.0 m thick; poorly sorted; 

clasts mostly of volcanic flow rocks; interbedded sandstone; weathers to grassy slopes; clasts up to 20 m in 

diameter, average 5-10 em; clasts subangular to subCumulative thickness 

above base of section 

(m) 

rounded ----------------------------------------------------------------------------------------------------------186 

9. Basalt, very dusky red; weathers reddish brown; glomerophyric with phenocrysts of plagioclase 3-4 em in length; 

medium grained groundmass ------------------------------------------------------------------ 110 

8. Conglomerate; same as unit 10 ------------------------------------------------------------------107 

7. Basalt, greenish-black and dusky-red; weathers dark yellowish brown and pale redish brown; porphyritic, with 

feldspar phenocrysts 0.3-1.0 em in length; flows 3-8 m 

thick; medium-grained groundmass; forms rounded outcrops ---------------------------------------------------------------------------------------------------------------- 87 

6. Conglomerate, dusky-red; weathers pale reddish brown; 

graded to sandstone in beds 2-4 m thick; poorly sorted; 

subangular to subrounded clasts, up to 10 em in diameter; 

clasts mostly dusky-red, greenish-black, and pale-green 

volcanic flow rocks ------------------------------------------------------------------------------------ 55 

5. Basalt, greenish-black; weathers yellowish brown; nonporphyritic; individual flows 2-4 m thick; forms rounded 

outcrops ---------------------------------------------------------------------------------------------------- 36 

4. Conglomerate; same as unit 6 ----------------------------- __ _____________________ 22 

3. Basalt, very dusky red; weathers dusky brown; porphyri-
42 SEVEN DEVILS GROUP, IDAHO AND OREGON 

Reference section, Doyle Creek Formation-Continued 

Unit Description 

3. Basalt, etc.-Continued 

tic, with phenocrysts 0.2-1.0 em in length; amygdules 

Cumulative thickness 

above base of section 

(m) 

filled with chlorite; individual flows 1.5-4 m thick ------------------------ 20 

2. Conglomerate; same as unit 6 -------------------------------------------------------------------- 8 

Wild Sheep Creek Formation 

1. Basalt, greenish-black; weathers dark yellowish brown; 

porphyritic, amygdaloidal; individual flows 1.5-4.5 m 

thick ---------------------------------------------------------------------------------------------------------------- 23 

Thickness of the Doyle Creek Formation at this reference section is 186m. The top of 

the formation is not exposed. 

The Doyle Creek Formation and its correlative units can be 

mapped over a wide area in northeastern Oregon and western 

Idaho. It has an estimated thickness of about 500 m. 

Flow rocks mostly are porphyritic and coarsely porphyritic 

metamorphosed basalt, basaltic andesite, andesite, and dacite 

(many are now spilite and keratophyre). Phenocrysts are set in 

pilotaxitic, intergranular, and intersertal groundmasses. Dominant components are plagioclase, ranging from albite to 

labradorite in composition, clinopyroxene, magnetite, and 

hematite (table 8). An altered iron-rich glassy groundmass makes 

up from 5 to 60 percent of some flow rocks. Secondary minerals 

epidote, chlorite, calcite, sphene, leucoxene, white mica, and quartz 

replace primary minerals and fill fractures and vesicles. The andesitic flow rocks are much more common than in older rocks and 

probably form as much as 50 percent of the flow rocks. They are 

light green and pale red and have plagioclase phenocrysts set in a 

recrystallized felty groundmass. 

Pyroclastic breccia and tuff constitute at least half of the clastic 

rocks in the type area. Farther north near Jim Creek, pyroclastic 

rocks are rare; most are epiclastic. Major components in the 

pyroclastic beds are metamorphosed basalt and andesite 

fragments, plagioclase, and pumice in a fine-grained red hematitic 

and glassy (altered in most thin sections) matrix. Many beds have 

abundant pumice fragments; in some, pumice forms reversely 

graded sequences. Tuff, as observed in 15 thin sections, consists of 

metabasalt and meta-andesite rock fragments (0-50 percent), 

pumice (0-9 percent), relict ash and glass (0-60 percent), 

plagioclase (3-35 percent), clinopyroxene (0-20 percent), and ironrich clayey matrix (0-40 percent). 

Epiclastic volcanic breccia forms thick beds. A good example is 
STRATIGRAPHY 43 

TABLE B.-Modal analyses of representative flow rocks from the Doyle Creek 

Formation 

[VB-105 groundmass of opaque minerals, clay, and feldspar; VS6-5 groundmass of altered tachylite; Tr., trace; 

1,000-1,200 points counted] 

Mineral 

Plagioclase phenocrysts 

Plagioclase microlites ... . 

Actinolite ........................... . 

Opaque minerals ............. . 

Quartz ·······-··-------------··---------

Epidote ----·---------·-----···---·--·--

Chlorite -·-----·------··----·-·-·----··-

White mica --·--·-···--·-··------·-·-

Calcite -----------·---·-·---·-····-···---

Groundmass ·-··-·-···-·--·--····· 

Total ···-·--·--·-··---------·--

VC-302 

(spilite) 

19 

28 

6 

Tr. 

1 

22 

19 

5 

VS6-5 

(spilite) 

9 

3 

------------------

4 

3 

------------------

------------------

Tr. 

6 

75 

VB-105 VC-218 

(keratophyre) (keratophyre) 

-------------------- 23 

48 69 

-------------------- Tr. 

14 4 

-------------------- ------------------

2 4 

Tr. ------------------

-------------------- ------------------

1 ------------------

35 ------------------ ---------------------------------------- 100 100 100 100 

exposed along the IP ALCO road near Kinney Creek directly 

underlying the Martin Bridge Limestone. A similar breccia unit in 

McGraw Creek that includes a few intercalated thin metabasalt 

flows is more than 70 m thick. Angular clasts of green, dark-gray, 

red, and dusky-red flow rocks are set in a dusky-red matrix. Some 

clasts are 30 em long, but most are from 2 to 8 em long. Sandstone, 

mostly arkosic wacke and graywacke, plus siltstone and argillite 

are important constituents in many sequences. Fine-scale crossbedding, flame structures, rip-up clasts, cut-and-fill structures, and 

graded beds are common sedimentary structures that indicate a 

relatively strong current regime during deposition. Quartz 

becomes a more important component volumetrically with 

increasing stratigraphic elevation. 

Conglomerate units are particularly noteworthy in the Doyle 

Creek Formation. Good exposures are found along the Oregon side 

of the Snake River, just below the contact with the Columbia River 

Basalt Group, in the drainage basins of Ashby, Dove, Leep, Thirty 

Two Point, and Jim Creeks. Conglomerate units are sequences of 

beds which include conglomerate as the dominant rock and 

subordinate amounts of flow rocks, volcanic breccia, and 

sandstone. In Ashby Creek, where a 186-m-thick conglomerate 

unit was measured and described, the rocks are conglomerate (50 

percent), flow rocks (42 percent), and breccia plus sandstone (8 

percent). The conglomerates generally are very poorly sorted, with 

angular to well-rounded clasts that range from 0.5 to 10 em in 

diameter. Metamorphosed basalt and basaltic andesite clasts are 

dominant (70 percent); keratophyric (15 percent), clastic (13 

percent), and plutonic (2 percent) clasts are subordinate. The 

increase in amount of plutonic clasts with stratigraphic elevation 
44 SEVEN DEVILS GROUP, IDAHO AND OREGON 

parallels the increase of quartz content in the sandstone. These 

conglomerate units are the oldest Upper Triassic beds that contain 

plutonic clasts. The Kurry Creek Member of the Doyle Creek 

Formation (see section "Kurry Creek Member") exposed at 

Pittsburg Landing and Upper Triassic conglomerate in the 

southern Wallowa Mountains (Prostka, 1963, p. 112) also have 

plutonic clasts. Plutonic clasts examined in thin section are 

metamorphosed microtonalite, quartz diorite, and gabbro. 

The rocks have been metamorphosed to an inequilibrium 

mineral assemblage in the greenschist facies. Primary plagioclase 

and ferromagnesian minerals are wholly or partly replaced by 

albite, epidote, chlorite, calcite, quartz, and zeolites, and groundmasses and matrices are hematitic and clayey. Morrison (1963, p. 

126-128) reported several varieties of zeolites in this formation. 

They are quantitatively minor and generally are associated with 

microcrystalline quartz as part of a sparse intergranular cement. 

Only analcime was observed in X-ray diffraction studies of rocks 

from the southern part of the mapped area. Chemistry of flow rocks 

indicate extreme mobility of ions, particularly the alkalis, during 

metamorphism (table 9). 

Most rocks in the formation were deposited in a marine environment, probably in relatively shallow well-oxygenated water near a 

landmass. Morganti (1972) suggested that some tuff outcrops in 

the upper part of the Eckels Creek drainage basin may have been 

subaerial eruptions. 

The Doyle Creek Formation most likely is Late Triassic 

(Karnian and possibly early Norian). Underlying strata in the 

TABLE 9.-Chemical analyses of representative flow rocks from the Doyle Creek 

Formation 

[Analyses by R. Batiza; see table 8 for rock types] 

Oxide VC-302 VS6-5 VB-105 VC-218 

Si02 -------------------------------------- 52.50 54.00 58.10 65.20 

Ti02 -------------------------------------- .80 1.76 1.54 .63 

Al203 ------------------------------------ 17.70 14.50 14.30 16.90 

FeO (total iron) ---------------- 8.20 9.28 9.91 3.21 

MnO -------------------------------------- .25 .12 .25 .06 

MgO -------------------------------------- 5.85 1.57 3.45 .02 

CaO -------------------------------------- 7.37 13.66 6.19 .75 

Na20 ------------------------------------ 4.14 .80 3.64 6.02 

K20 -------------------------------------- 1.28 .07 1.31 2.20 

P205 ------------------------------------ .31 .30 .20 .20 

H20 (total water) ------------ -------------------- 3.47 -------------------- ------------------

C02 -------------------------------------- -------------------- .28 -------------------- ------------------

Total -------------------------- 98.40 99.81 98.89 95.19 
STRATIGRAPHY 45 

Wild Sheep Creek Formation are Karnian, and overlying 

limestone in the Martin Bridge Limestone is Norian. Local 

correlative and partly equivalent strata are the so-called Lower 

Sedimentary Series and the upper part of the Clover Creek Greenstone (Prostka, 1963) in the Wallowa Mountains. 

KllRR Y CREEK MEMBER 

The name Kurry Creek Member is here given to a mainly clastic 

rock sequence within the upper part of the Doyle Creek Formation 

exposed in the Pittsburg Landing area west of White bird, Idaho. It 

replaces the name Pittsburg Formation (Wagner, 1945). Vallier 

(1968) and White (1972) described the rock unit in some detail and 

measured several stratigraphic sections. One of the stratigraphic 

sections, just southeast of West Creek, is selected as the type 

section even though the base and top of the member are not 

included (fig. 11). The rock unit is local and crops out only in the 

Pittsburg Landing area. It overlies, probably conformably, rocks 

of the Wild Sheep Creek Formation and is unconformably overlain 

0 .5 MILES 

0 1 KILOMETERS 

FIGURE 11.-Type section of the Kurry Creek Member of the Doyle Creek Formation 

measured along a spur southeast of West Creek. Base from U.S. Geological 

Survey Grave Point 71/z-minute quadrangle, 1:24,000, 1963. 
46 SEVEN DEVILS GROUP, IDAHO AND OREGON 

by mudstone, argillite, and graywacke of the Jurassic Coon Hollow 

Formation. 

Type section, Kurry Creek Member 

of the Doyle Creek Formation 

Location: Grave Point 7W quadrangle; NE% SE1/.i sec. 29, T. 27 N., R. 1 W., up major spur southeast of West 

Creek beginning at an elevation of 465m (1,520 ft)nearthejeeptrail, thencetothetopoftheridgeinSW%sec. 

28. Tape and Brunton method used. Assisted by David L. White. Neither the 

base nor top of member is exposed. 

Unit Description 

19. Pebbly sandstone, greenish-black; weathers dusky brown; 

coarse-grained matrix; lithic wacke with abundant clasts 

of volcanic rocks; weakly cross-laminated; angular to 

Cumulative thickness 

above base of section 

(m) 

subangular grains; some interbedded shale ...................................... 270 

18. Covered interval; probably shale .............................................................. 245 

17. Pebble conglomerate, dark-brown; weathers pale yellowish brown; poorly sorted; subrounded to well-rounded 

clasts 4-8 ern in diameter; matrix of coarse sand; grades 

upward to very coarse sand; clasts mostly of volcanic 

origin ................................................................................................................ 224 

16. Sandstone, lithic wacke, greenish-black; weathers yellowish brown; fair to moderate sorting; coarse grained; 

weakly cross bedded; some grading to siltstone ................................ 221 

15. Mudstone, dark-brownish-green; weathers pale brown; 

friable; some thin beds of fine-grained sandstone .......................... 206 

14. Sandstone; same as unit 16; some mudstone and siltstone 

beds up to 2 rn thick; slope partly covered ........................................ 204 

13. Mudstone; same as unit 15 .......................................................................... 178 

12. Conglomerate, dark-brown; weathers pale yellowish brown; 

pebble-sized clasts of volcanic origin; well rounded ...................... 173 

11. Covered interval; seems to be a sequence of alternating 

sandstone and mudstone .......................................................................... 172 

10. Sandstone; same as units 14 and 16 ........................................................ 165 

9. Pebble conglomerate, grayish-green; weathers pale brown; 

poorly sorted; clasts subrounded to well rounded; matrix 

mostly of sand; volcanic flow rocks make up all clasts; 

weakly bedded .......................................... -.................................................... 156 

8. Pebbly mudstone, grayish-green; weathers pale brown; 

well-rounded clasts up to 3 ern in diameter in a finegrained matrix; very poorly sorted; pebbles constitute 

about 10 percent of the unit; 3-rn conglomerate bed 6 rn 

above base of unit; most clasts are porphyritic volcanic 

flow rocks ...................................................................................................... 154 

7. Conglomerate, dark-brown; weathers pale yellowish brown; 

cobble to pebble sized; interlayered sandstone and mudstone (10-15 percent) are tops of graded sequences; clasts 

are well rounded; some units are grayish red; fine-grained 

beds are mostly covered by soiL ............................................................ 120 

6. Conglomerate, dark-brown; weathers pale brown; cobblesize clasts, average 8-12 ern in diameter; clasts are 
STRATIGRAPHY 47 

Type section, Kurry Creek Member 

of the Doyle Creek Formation-Continued 

Unit Description Cumulative thickness 

above base of section 

(m) 

6. Conglomerate, etc.-Continued 

mostly porphyritic volcanic flow rocks; some inter layered 

sandstone; weak bedding-------------------------------------------------------------------------- 62 

5. Mudstone and sandstone, greenish-black and dark-brown; 

weathers dark yellowish brown and pale brown; mudstone beds 10-50 em thick are interlayered with 1-5-cmthick sandstone beds; mudstone is friable and has pencil 

cleavage; Halobia abundant on some bedding planes, 

poorly preserved ______ .. ____ .. __ ..... _____________________ .... _______ ........ _____ ..... _____ .... _________ . 58 

4. Covered interval; probably mostly mudstone -------------------------------------- 43 

3. Conglomerate; dark-green matrix; weathers pale brown; 

sand-sized matrix with clasts up to 35 em in diameter; 

average clast size range is about 3-10 em; clasts subrounded to well rounded; contains thin beds of coarse 

sandstone, some weakly cross-laminated; clast count 

shows dark nonporphyritic volcanic flow rock (36 

percent), porphyritic flow rocks ( 40 percent), volcaniclastic rocks (14 percent), and unknowns (10 percent) ____________________ 34 

2. Mudstone and sandstone; same as unit 5 _________ ----------------------------------- 26 

1. Conglomerate; same as unit 3 ------------------------------- ------------------------------------ 16 

Base of section is not the base of the rock unit 

Total thickness measured is 270 m. 

The Kurry Creek Member is almost entirely clastic rocks, which 

makes it easy to distinguish from other rocks in the Snake River 

Canyon region. Rocks are conglomerate, sandstone, tuff, shale, 

argillite, and limestone. Conglomerate is common and mostly 

consists of thick beds or sequences of conglomerate beds 

interlayered with sandstone and shale. Conglomerate beds 

generally contain poorly sorted materials whose clasts range from 

angular to well rounded. They generally are crudely graded; some 

are cross-laminated with steeply dipping foreset beds. These are 

particularly noticeable where there is a large percentage of sandsized matrix. Clast compositions are mostly volcanic flow rocks 

and volcaniclastic rocks, although some beds contain as much as 3 

percent plutonic clasts (metamorphosed quartz diorite, trondhjemite, and gabbro). 

Sandstones are volcanic wackes (classification of Williams and 

others, 1954). Colors are dark brown on fresh surfaces and light 

brown on weathered surfaces. Many sandstone beds are the upper 

parts of graded units, whereas others occur as individual beds. 

Components are volcanic rock fragments, plagioclase, and quartz 

in a matrix of clay, chlorite, plant fragments, calcite, feldspar, rock 
48 SEVEN DEVILS GROUP, IDAHO AND OREGON 

fragments, and iron ores. Shale units also are dark brown on fresh 

surfaces; the more calcareous beds are lighter brown. Wood 

fragments are common constituents in shales at the top of graded 

sequences. Species of Halobia are occasionally observed along 

bedding planes. Limestone beds are argillaceous and carbonaceous; most have a strong fetid odor on fresh breaks. 

Tuffs are abundant. Many are basaltic in composition, and some 

have much glass and palagonite. One tuff unit, exposed along the 

road between Pittsburg Landing and Whitebird, Idaho, is 

composed of basalt rock fragments, labradorite, and augite in an 

iron-rich glassy and clayey matrix. Grains are sand sized, angular, 

and fresh. 

The rocks were deposited in a marine environment very near a 

landmass. Because of its local outcrop area and stratigraphy, the 

member probably represents a submarine inner fan, following the 

model of Walker (1975), that formed in relatively shallow water 

near a rugged landmass. 

The Pittsburg Formation was thought to be Carboniferous by 

Wagner (1945). Recent identifications of ammonites and Halobia 

by N. J. Silberling (unpub. data) indicate a Late Triassic (late 

Karnian to middle Norian) age for the Kurry Creek Member. 

Correlative and probably partly equivalent rocks are the so-called 

Lower Sedimentary Series of Smith and Allen (1941) and the upper 

part of the Clover Creek Greenstone (Prostka, 1963). 

MARTIN BRIDGE LIMESTONE 

The Martin Bridge Limestone lies stratigraphically above the 

Seven Devils Group. Exposures of the formation are widely distributed in northeastern Oregon, western Idaho, and extreme 

southeastern Washington. Earlier studies of the formation in the 

Snake River Canyon area are those by Lindgren (1901), Ross 

(1938), Laudon (1956), Cannon (see Hamilton, 1963a), and Vallier 

(1967). Hamilton (1963a) renamed the Martin Bridge Formation 

the Martin Bridge Limestone. 

The formation is well exposed on both sides of the Snake River at 

Big Bar just south of Kinney Creek and near the mouth of the 

Grande Ronde River. The best stratigraphic section is along the 

south side of Kinney Creek, where about 530 m of limestone and 

dolomite is exposed (Vallier, 1967). Strata of this formation also 

crop out on the ridge between Limepoint and Indian Creeks near 

the Kleinschmidt Grade, a road that connects the IP ALCO road 

with Cuprum, Idaho. At this locality, the Martin Bridge Limestone 

seems to be in depositional contact with the underlying Doyle 
STRATIGRAPHY 49 

Creek Formation on the east but in fault contact with that 

formation on the west. 

In the Snake River Canyon the basal unit of the formation 

consists of grayish-green calcareous graywacke, siltstone, and 

argillaceous limestone that ranges from 0 to 5 min thickness. This 

basal unit overlies a thick volcanic breccia of the Doyle Creek 

Formation in Kinney Creek, Hibbles Gulch, and McGraw Creek. 

Rock fragments in the green calcareous graywacke are similar to 

underlying rocks of the Doyle Creek Formation. Because the basal 

beds thicken and thin and bee a use they overlie different rock types 

within the Snake River Canyon, the contact is likely an 

unconformity. The upper contact is not exposed in the Snake River 

Canyon. However, in the Wallowa Mountains the Martin Bridge 

Limestone grades upward into the Hurwal Formation (Smith and 

Allen, 1941) through a series of alternating limestone and shale 

units. 

Rock types are limestone (sparite, biosparite, and micrite), 

dolomite, and limestone breccia. Some thin beds of calcareous 

shale are inter layered, but these make up a very small part of the 

unit. Colors are gray, brownish gray, and black on fresh surfaces 

and light gray to white on weathered surfaces. Beds range in 

thickness from 30 em to 20 m but average about 1.5-2 m; thickest 

units, massive brecciated partly dolomitized limestone, represent 

high-energy depositional environments. Other units consist either 

of thinly laminated carbonaceous argillaceous limestone or of 

massive recrystallized limestone. Studies of24 rock samples show 

that insoluble residues, mostly clay (illite) and carbon, account for 

1-21 percent of the rocks by weight. Dolomiteinfiveofthe samples 

ranges from 0 to 95 percent. 

There is a general scarcity of terrigenous materials, except for 

illite and occasional feldspars, in the limestone above the basal 

unit, which suggests either that the sediments were deposited far 

from a terrigenous source or that the area was protected by barriers 

to coarse sediment. There are no definite reef facies in the Snake 

River Canyon exposures. Fossils do indicate a shallow-water 

environment, and thick massive units are recrystallized breccias. 

N olf (1966) reported a reef facies in the northern Wallow a 

Mountains, and Laudon (1956) interpreted the sequence in the 

Snake River Canyon as well-defined reef limestone. The Martin 

Bridge Limestone seems to fit Wilson's (1974) type II carbonateplatform margin, which consists of knoll-shaped reefs on gentle 

slopes of a continental shelf. 

A well-preserved silicified fauna includes ammonites typical of 
50 SEVEN DEVILS GROUP, IDAHO AND OREGON 

the Mojsisovicsites kerri Zone of earliest Norian (Late Triassic) age 

(N.J. Silberling, writtencommun., 1965). Correlative and probably 

equivalent units are found in several localities within the region: 

in the Wallow a Mountains, in the eastern part of the Seven Devils 

Mountains north of Riggins, Idaho, and near the mouth of the 

Grande Ronde River in southeastern Washington and western 

Idaho. In all localities, except at Big Bar in the Snake River 

Canyon, the limestone grades upward into a black shale, 

sandstone, and mudstone unit which is known as the Hurwal 

Formation in the Wallowa Mountains and as the Lucile Slate in the 

Riggins area of western Idaho. 

HURW AL FORMATION 

The Hurwal Formation (Smith and Allen, 1941) was described in 

the Wallow a Mountains as a shale and limestone unit of Late 

Triassic age that overlies the Martin Bridge Limestone. N olf (1966) 

found Early Jurassic fossils in the Hurwal Formation of the 

northern Wallowa Mountains. In the Snake River Canyon, the 

H urwal Formation has been mapped only near the mouth of the 

Grande Ronde River (Glerup, 1960), where two distinct lithologies 

occur. The lower unit is made up of metamorphosed argillaceous 

limestone and argillite, and the \lpper unit consists of metamorphosed mudstone and volcaniclastic rocks. No fossils were 

found in the formation in the Snake River Canyon, and it is 

regarded as Late Triassic age in the report area. 

COON HOLLOW FORMATION 

Morrison (1964) described the Coon Hollow Formation and 

designated the ridge south of Little Cougar Creek, southern Nez 

Perce County, northwest Idaho (Jim Butte Creek 71/z-minute 

quadrangle), as its type section. The formation is well exposed at 

Coon Hollow, Oreg., on the opposite side of the Snake River 

Canyon, for which it was named. Near the Washington-Oregon 

boundary, thin-bedded sequences within the formation are folded 

about northeast-trending axes. Another probable exposure of the 

formation is at Pittsburg Landing along the south side of Pittsburg 

Creek in Oregon. 

The Coon Hollow Formation is easily distinguished from other 

formations. Rocks weather rapidly, and the exposures are 

characterized by rounded slopes, in strong contrast to the rugged 

outcrops that characterize older formations. The lower and upper 

boundaries are angular unconformities. In the northern part of the 

area, the Coon Hollow overlies a truncated section of the Wild 

Sheep Creek Formation; at Pittsburg Landing it overlies the Kurry 
STRATIGRAPHY 51 

Creek Member of the Doyle Creek Formation. It is overlain by the 

Columbia River Basalt Group. 

The Coon Hollow Formation probably was much more extensive 

before Nevadan deformation and late Mesozoic and early Tertiary 

erosion. Deep weathering and folding prevented satisfactory 

thickness measurements, but Morrison (1964) estimated the 

thickness to be about 600 m. 

Rock types are primarily black and dark-brown mudstone with 

minor siltstone and sandstone. Rare beds of conglomerate and 

breccia also occur in the sequence. Bedding is defin~d by lightcolored calcareous siltstone lenses less than 2 em thick interlayered every few centimeters throughout many of the mudstone 

units. The mudstone is well indurated and forms distinct beds as 

much as 20m thick. Most sandstone and siltstone beds range from 

1 to 35 em in thickness and generally are graded. A basal conglomerate that overlies truncated Upper Triassic strata in the type 

area contains clasts that are mostly of sedimentary origin; 

volcanic clasts are less common. 

Fossils are rare in the Coon Hollow Formation. Euxinic 

conditions discouraged the development of benthonic faunas, and 

deep weathering and fracturing presumably have destroyed 

fossils. R. W. Imlay reported (Morrison, 1964) that one fossil locale, 

about 125m above the base of the formation in the type area close 

to the Washington-Oregon boundary, contains fragments of the 

ammonite genus Cardioceras, which is diagnostic of the lower part 

of the Upper Jurassic Oxfordian Stage in Europe. From exposures 

of probable Coon Hollow beds near Pittsburg Landing, Imlay 

identified ammonites of the Middle Jurassic Callovian Stage 

(written commun., 1968). 

R. W. Imlay (oral commun., 1976) pointed out that the rock unit 

exposed at Coon Hollow, which contains an Oxfordian ammonite 

fauna 125 m above its base, may not be correlative with the rock 

unit exposed near Pittsburg Landing, which contains a Callovian 

ammonite fauna near its base. For purposes of this report, 

however, the two units are considered to be largely correlative for 

two major reasons: (1) Their lithologies are not easily differentiated in the field and (2) Callovian strata might be present 

below the Oxfordian beds in the type area. Certainly, these strata 

deserve much closer scrutiny to determine the relationships. 

TERTIARY BOULDER BEDS 

A profound unconformity separates the pre-Tertiary rocks from 

the Miocene basalt flows. The old surface of erosion is visible along 

most parts of the canyon. Where the basalt has only recently been 
52 SEVEN DEVILS GROUP, IDAHO AND OREGON 

stripped away, the old erosion surface is overlain by boulder and 

cobble beds. The boulder beds are well exposed just south of the 

Grande Ronde River in Washington, where the thickness is as 

much as 10m. Compositions are quartzite, pre-Tertiary flow rocks, 

and unmetamorphosed granitic rocks. Farther south along the 

unconformity in several places, quartzite boulders are the only 

ones present; best outcrops of these boulders are on the eroded 

surface of the Martin Bridge Limestone near McGraw Creek. The 

source of the cobbles and boulders apparently is some of the 

Precambrian quartzites that are exposed farther east in Idaho and 

the meta volcanic and granitic rocks that were derived locally from 

the Seven Devils Group and the Idaho and Wallowa batholiths. 

COLUMBIA RIVER BASALT GROUP 

The Columbia River Basalt Group is well exposed in the Snake 

River Canyon, particularly along the western side in Oregon. This 

rock unit was originally named the Columbia Lava by Russell 

(1893) for supposed Eocene through Pliocene basalts of the 

Columbia Plateau in Washington and Oregon. Merriam (1901) 

restricted the name to lavas of post-John Day andpre-Mascall age. 

Waters (1961) divided the rock unit into the Picture Gorge Basalt 

and the overlying Yakima Basalt on the basis of distinctive 

outcrop and mineralogic and chemical differences. He traced these 

formations from central Oregon to the Imnaha River in eastern 

Oregon. Brown and Thayer (1966) changed the name Columbia 

River Basalt to the Columbia River Group and included the Picture 

Gorge Basalt, Mascall Formation, the "rhyolitic marginal facies" 

that is transitional with the Strawberry Volcanics, and the 

Yakima Basalt. Griggs (1976) renamed it the Columbia River 

Basalt Group, restricting the name to predominantly basaltic 

rocks so as to include the Picture Gorge and Yakima Basalts and 

to exclude the Mascall and rhyolitic rocks. For purposes of this 

report, where stratigraphic relationships and lithologic affinities 

to the type area are still unclear, the name Columbia River Basalt 

Group is retained. 

Along the Snake River Canyon two mappable units are present, 

an older one that has mineralogic and outcrop characteristics 

similar to those of the Picture Gorge Basalt, and a younger one 

similar to the Yakima Basalt as described by Waters (1961). For 

purposes of this report, however, the basalts are referred to as the 

lower unit and upper unit. 

The lower unit is composed of flows that are mostly porphyritic 

basalt. It weathers to gentle slopes, and the rocks have a 

distinctive waxy luster on fresh surfaces. The thickest sections, 
STRATIGRAPHY 53 

which range from 200 to 450 m, are exposed near the mouth of the 

Imnaha River and in the canyon of Pine Creek just southwest of 

Oxbow, Oreg. The earliest flows were extruded over an irregular 

topography that had a regional relief of 500-700 m. The lower unit 

is very well exposed along the Oregon side of the Snake River 

Canyon between Saddle Creek and the mouth of the Imnaha River. 

The contact between the lower and upper unit is marked by a 

change in topography from the gentle slopes of the lower unit to the 

steep slopes of the upper unit. At places this break is marked by a 

line of vegetation. 

Flows of the upper unit are exposed in excellent outcrops 

throughout the area and just south of Saddle Creek for several 

kilometers. They are the only flows that cap the old topography. 

This suggests that the lower unit accumulated in low areas around 

topographic highs, leaving the highs as steptoes until covered by 

flows of the upper unit. The maxim urn thickness of the upper unit is 

about 900 m near the mouth of the Grande Ronde River. 

Bingham and Grolier (1966) dated the upper unit as late Miocene 

and early Pliocene. However, recent radiometric dating appears to 

restrict the age of the Columbia River Basalt Group to the middle 

Miocene. Baksi and Watkins (1973) compiled a synthesis of 

potassium-argon dates from nine sections in northeastern Oregon, 

western Idaho, and south-eastern Washington. The age range of 

112 dates is 13.5t...0.3 million years to 15.4t...0.3 million years for 

flows throughout that region, which is in the early middle Miocene 

Epoch (time scale of Berggren, 1972). Although no dates have been 

published for rocks in the area considered here, a Miocene age is 

adopted for the Columbia River Basalt Group in the Snake River 

Canyon included in this report. 

QUATERNARY DEPOSITS 

Most Quaternary sedimentary deposits are thin and discontinuous in the Snake River Canyon region and can be broadly 

divided into glacial, landslide, terrace, and alluvial fan deposits. 

Glacial deposits occur at higher elevations in the Wallowa and 

Seven Devils Mountains, and some morainal materials extend 

down to an elevation of about 1,200 m (4,000ft). Landslides formed 

some major topographic features along the Snake River Canyon 

(Vallier and Miller, 1974). The largest of these is at Big Bar, where a 

slide from the west wall of the canyon apparently dammed the 

river. A remnant of that landslide parallels the river for nearly a 

kilometer and rises 60 m above the valley floor. It is presently 

almost entirely submerged beneath waters backed up by Hells 

Canyon Dam. Other major landslide deposits are near the mouth 
54 SEVEN DEVILS GROUP, IDAHO AND OREGON 

of Copper Creek, about 14 km north of Homestead, at Johnson Bar, 

and at Pittsburg Landing. Terrace deposits in the Snake River 

Canyon occur primarily at Pittsburg Landing, Johnson Bar, 

Temperance Creek, and Big Bar. All have formed in wide parts of 

the river valley, and in places three levels have been identified. The 

highest may be related to the Bonneville Flood. Terraces are the 

result of rapid accumulations of debris (landslide, flood gravels, 

and alluvial fans) with subsequent smoothing by high water. 

Deposits of alluvium form fans all along the Snake River Canyon 

where tributary streams debouch into the Snake River. 

CONCLUSIONS 

A composite diagram of columns shows the inferred stratigraphic relations in the Snake River Canyon (fig. 12). Important 

interpretations are the following: (1) Permian strata are confined 

to the southern part of the area; (2) there is an increase in clastic 

content of the Wild Sheep Creek Formation toward the north along 

with a general thinning; (3) the Wild Sheep Creek Formation 

overlies gabbro, amphibolite, mylonite, and plagiogranite to the 

north, but overlies Permian strata to the south; ( 4) the Martin 

Bridge Limestone is not ubiquitous but overlies the Doyle Creek 

Formation near Kinney Creek and near the mouth of the Grande 

Ronde River; it is absent in the Pittsburg Landing area where 

Jurassic strata overlie the Upper Triassic Doyle Creek Formation; 

and (5) near the Grande Ronde River mouth the Hurwal Formation 

of presumable Late Triassic age overlies the Martin Bridge 

Limestone. Just a few kilometers south, in extreme northeastern 

Oregon, the Martin Bridge Limestone and Hurwal Formation are 

absent, and Jurassic strata directly overlie the Wild Sheep Creek 

Formation. 

The pre-Tertiary stratigraphy in the Snake River Canyon attests 

to the presence of old island arc systems, which are the result of 

volcanism, tectonism, and sedimentation at converging plate 

boundaries. In this area an old Pacific plate presumably collided 

with the northwestward-moving North American plate. The 

convergence and resultant subduction created the Permian and 

Upper Triassic island arc, and later subduction probably led to 

the Idaho batholith magmatic event. 

The silicic PermiBlil strata were part of an early volcanic arc 

which formed on crust of unknown nature. These volcanic flows 

and associated clastic rocks are correlative with the Lower 

Permian limestone blocks of the Elkhorn Ridge Argillite. Most of 

the Permian island arc deposits have been subducted or eroded, 

and only small remnants still occur in the region. 
Oxbow 

area 

Tcr 

Phc 

~?-

Pwr 

,?~ II)) )) 

~II ~II ~y? ~ 

Homestead 

Creek 

Tcr 

liws 

Phc 

\\~ 

"'~? 

\ 

\ 

\ 

II 

,, 

\ 

\ 

\ 

\ 

\ 

I 

\ 

\ 

I 

Kinney 

Creek 

Tcr 

limb 

fide 

RWS 

Phc 

~ 

/ 

/ 

/ 

/ 

/ /, 

/ 

/ 

,;? 

Battle 

Creek 

Tcr 

fide 

RWS 

~ 

--- - -- ------

Pittsburg 

Landing 

Tcr 

Jch 

fide 

RWS 

m ?.r 

? ? ? ? 

--------

------

--------

Jim 

Creek 

Tcr 

Jch 

fide 

RWS 

»» 

?/ 

""""--:::...-

--- --- --

Grande 

Ronde 

River 

Tcr 

lih 

r-?-

limb 

fide 

liws 

./?Vi~ 

EXPLANATION 

~ Columbia River Basalt Group 

~ Coon Hollow Formation 

G Hurwal Formation 

I limb I Martin Bridge Limestone 

~ ~ Doyle Creek Formation 

I 

I 

I 

I 

~1~ Wild Sheep Creek Formation 

(.? ~ • 

.!!!. ~ Hunsaker Creek Formation ·:;: 

~ ~Windy Ridge Formation 

~ 

~ mmmru Basement complex 

--~ Unconformity 

1 20 KILOMETERS 

0 MILES 

en 

Ll..l 

a: ....J L.LJ -

f- ::;;,;; w 

::;;,;; '-'? 0 

....J 

;;;2 

FIGURE 12.-Composite stratigraphic diagram showing stratigraphic relations in Snake River Canyon between 

Oxbow, Oreg., and the mouth of the Grande Ronde River. 

I 

0 

0 

z 

0 

8 

00 

8 

z 

00 

01 

01 
56 SEVEN DEVILS GROUP, IDAHO AND OREGON 

The more mafic Upper Triassic volcanic arc formed on the older 

arc. Along the southern part of the area described in this report, 

Upper Triassic volcanic rocks overlie Permian strata; farther 

north they overlie "basement" that is a composite of plutons (gabro 

and quartz diorite) and amphibolite-facies rocks that probably are 

older metamorphosed sediments and volcanic rocks. The Triassic 

volcanic rocks were capped by Norian platform limestone and 

associated basin facies. 

During the Jurassic, flyschlike deposits were laid down in arcrelated basins in part contemporaneous with culminating orogenic 

phases, regional metamorphism, and early plutonism that 

subsequently led to the formation of batholiths in northeastern 

Oregon and western Idaho. 

Culminating pulses of the Nevadan orogeny uplifted and 

exposed the rocks, which were deeply eroded during Cretaceous 

and early Tertiary time. Flows of the Columbia River Basalt Group 

covered the irregular topography during the Miocene Epoch. 

Basin-and-range faulting, regional uplift, and erosion formed the 

present topography during late Miocene through Pleistocene time. 

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58 SEVEN DEVILS GROUP, IDAHO AND OREGON 

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