International Geological Congress $ V I session S 1 93 3 United tates ,

— Guid eb o o k 2 1 : E xcurs io n C 2

CE N T RA L O R E G O N

RALPH W . CHAN E$ UNIV ERS IT$ OF CALI F ORNIA

UNITED STATES

$ V M T PRINTING OFFI CE GO ERN EN u WASHINGTON 193 2 T his guidebook is published under the auspices of the United States S ’ G eological urvey, but it is not a part of the Geological Survey s s x regular series of publication , and the opinions e pressed in it and the use of nomenclature do not necessarily conform to Geological Survey u sage .

I I CONTENTS Page Foreword G eneral geography Geology Itinerary Bibliography

ILLUSTRATIONS

P LATE 1 . Map of central Oregon

2 . A B B V M Ke nzie , elknap Crater ; , iew from c Highway

3 . A x , John Day formation e posed on John Day Highway; B V M , iew northwest from the ascall ranch

CE NTRAL OR EGON

By RALPH W . CHANE$

FOREWORD In the preparation of this summary of the geology and paleon tology of central Oregon the writer is particularly indebted to

Dr . Edwin T . Hodge , of the University of Oregon , for data regarding the history of the Cascade Mountains and the region

. . B uwa ld a . S to the east . Dr John P and Dr Chester tock , of the California Institute of Technology , have also furnished material of value , and the published work of Dr . Earl L .

. . S Packard and Dr Warren D mith , of the Univers ity of Oregon , has been drawn on extensively . The studies of Dr . John C . Merriam in the John Day Basin and elsewhere in eastern 30 Oregon , which were begun more than years ago and have continued down to the present time , have served as a basis for the work of the writer in Oregon and for the preparation of this guidebook . The trip across Oregon from Eugene to Arlington traverses one of the most extensive regions in western America where continental deposits are predominant and where the record of land animals and plants during the Tertiary period is compara tivel y complete and well known . This region also represents a center of volcanic activity which has extended from the Terti ary down almost into historic times . The Cascade Range , which in its present development originated in later Tertiary time , illustrates the tectonic and volcanic history of Oregon , and its profound influence upon the life both of the Tertiary and the Recent 1 s at once apparent . S From Eugene , the site of the tate University of Oregon , in ' - et i the Willamette (wil lam ) Valley, the excurs on crosses the Oc ho co Cascade Mountains , the Madras Upland , the Moun tains , the John Day Basin , and the Columbia River Lava

1 . Plateau , as indicated on Plate

GENERAL GEOGRAPH$ S mith has pointed out the twofold character of the S climate of Oregon , that in the western part of the tate being marine and that on the east side of the Cascade Range of a

1 — 1 3 14 . Numbers in parentheses refer to bibliography, pp . 2 xvr I NT E R NA TI ONA L GE O LOGI CA L CONGR E S S

As continental type . regards both temperature and rainfall , these mountains act as a barrier that limits the mild moist climate to the western third of the State . Along the coast the 100 annual rainfall may exceed inches meters) , but in most of eastern Oregon it is only 1 0 to 1 5 inches to f 1 n meter) . The di ference climate between the west and the east sides of the Cascade Range is indicated by the great dis similarity of the forests in a traverse across the State . In the coastal region and from the Willamette Valley up to the crest of the mountains a dense growth of Douglas fir (P n udotruga taxzf oli a ) and associated conifers will be seen ; east of the moun tains the yellow pine (Pi n u: ponderos a ) extends for a consider able distance out on the Madras Plain , but elsewhere true forests disappear except on the summits of the Ocho co Mountains and other inland ranges ; the uplands are occupied by scattered junipers (juniperur) and sage and along the P o ul a r S alix streams there are cottonwoods ( p ) and willows ( ) . Sheep and cattle raising is the principal occupation of the rather sparse population of eastern Oregon , but excellent high ways and the extension of railroads into this part of th e

State are tending to diversify the activities of its inhabitants .

In western Oregon ranching of various types , fruit raising, and lu mbering are active industries , and lumbering is also impor tant along the east crest of the Cascades .

GEOLOG$ — e r General f a tu er . The rocks of the Coast Range are largely i n marine sediments of Tertiary age , with basaltic and other trus ions and with intercalated flows and pyroclastic rocks .

The Coast Range represents an anticlinorium , with the steepest folds on the west side and with the Willamette Valley cut into ff the soft Oligocene tufis on its eastern slopes . These tu s dip eastward under the Cascade Range and according to Hodge (14) are a part of a block or series of blocks , including much of north western Oregon , which were elevated during Pliocene time along their western edge , with perhaps a fault along the coast . Early Tertiary marine invertebrate faunas have been studied in thi s s area west of the Cascade Range, and near Goshen , a few mile south of Eugene , a lower Tertiary flora contains species whose nearest living equivalents are now found in the low latitudes of both hemispheres . The Cascade Range l n most of Oregon 1 s made up largely of the Columbia River lava , of Miocene age . This volcanic series , which reaches a maximum thickness of about feet ' e i s met rs) , rests upon the Oligocene tufis and sediments and inclined eastward across the range , farther east it is faulted down CENTRAL OR E GON 3 and extends for the most part in horizontal structure over the 14 f State and into Idaho . Hodge ( ) has urnished the following section for the Cascades l Recent : Lava flows from acidic to basic ; pyroc astics and stream deposits . : R e c Pleistocene Andesites of Cascade ang , including basaltic and andesiti 2 fl f . ows and interbedded ashes and tu fs Madras formation , torrential stream

s . depo its , lake beds , and lava flows

Pliocene : Erosion and deformation .

: R . Miocene Columbia iver lava , basaltic flows

: tufis . Oligocene Cascadia formation, a thick series of agglomerates and Eo : H of cene ighly deformed rhyolitic material , similar to Clarno formation

eastern Oregon , has been found in some of the deep streams cut in the west R R side of the Cascade ange, notably at Cascadia , on the Santiam iver .

East of the Cascade Range , as well as in the range itself, the Columbia River lavas are the most conspicuous and extensive series . Where there has been folding, erosion b y the larger streams has exposed the underlying rocks , as in the John Day

Basin ; only along the lines of the major structural features , Ocho co such as the Mountains , have the Columbia River lavas been extensively removed . The following section is based on Merriam ’ s original section in the John Day Basin slightly B uwa ld a modified by the work of , Hodge, Packard , and the writer to include the area a djo i n ing t hi s traverse .

2 The Madras formation of Hodge includes the upper Miocene Dalles and Hood River formations of Buwa lda and Moore and the Pleistocene Deschutes

. E . T . formation of Russell and Stearns See Hodge, , Framework of Cascade

: 49 . 3 50 1928 R I . C . Ranges in Oregon Pan Am . Geologist, vol . , p , June, ; ussell , , 252 o : . . . B . Ge logy and water resources of central Oregon U S Geol Survey ull ,

. 90 1905 T . Des p , ; Stearns , H . , Geology and water resources of the middle - R B 63 7 . : . . . chutes iver asin , Oregon U S Geol Survey Water Supply Paper , p 1 3 3 w ~ 193 1 Bu ald a . P . B . N . The , ; , J , and Moore, , Dalles and Hood River for b 404 mat ons an the Columb a ve go e : Ca ne ie Inst . Wash ngton Pu . , i — d i Ri r rg r g i . 1 3 26 1930 S new . . 66 . 236 . 9 1 927. p p , , and cience , ser , vol , p , Sept , 4 $ V I INTERNATIONAL GEOLOGICA L CONGRES S

Geol ogi c recti on f or central Oregon

Fo rmatio n Li tho logy

Alluvium and terrace de posits Sand and gravel .

Glacial deposi ts . Andesitic and rhyolitic f flows , dacites , and tu fs R of Cascade ange .

a Sand , gravel , and lav Madras formation . flows .

R k attlesna e formation .

’ Tufl , ash , and possibly Mascall formation . gravel .

’ ufi li ine basalt, t , an Columbia River lava O v d gravel .

T f a s h c u f, , and rhyoliti John Day fo rma tl o n . tuff and flows .

c Shale , tuff, and rhyoliti Clarno format1ou . and andesitic flows .

' ' S andstone , conglomerate , Chl co fo rm a tl o n and shale .

a k fine- a ne shale P f rm a r n D r gr i d Horsetown o t o . and sandstone .

Silvies River beds ; un Red impure limestone . name be s in Oc ho co d d B atholith 1 c 1 ntrus ro ns Mountains and on low ; gra no d1or1 te . er Silvies River .

Calcareous shale , lime

Ma rtm B r1d c i . ba g format on stone , agglomerate , ff salt , andesite , and tu .

P a e z — l o oi c . There are thick Carboniferous and Permian rocks in the Wallowa Mountains and Elkhorn Ridge . — i a Tr s s i c a nd jura rri c . Invasions of the sea into eastern Oregon during Triassic and Jurassic time resulted in the shore line deposition of sediments , which have been subsequently folded and eroded . The Wallowa Mountains , in the north S eastern part of the tate , were uplifted late in the Jurassic CENT

C ENTRAL OREGON 5

re r p eriod , when the were also extensive intrusions of granula rocks ; the principal metallic deposits of northeastern Oregon a re related to these intrusives . The present topographic relief of the Wallowa Mountains is due to uplift in late Pliocene or early

Pleistocene time . — r a c us . C et eo The Cretaceous seas came in from the west , pos i l e s b y during late Horsetown time , and reach d their maximum extension in the Chico epoch . They deposited a thick series of c shales , sandstones , and conglomerates , of whi h the most exten o n th sive outcrop is in the Mitchell quadrangle , the axis of e

Mitchell anticline . They are well exposed on the highway below

Mitchell . A rich ammonite fauna from these beds has been studied by Packard who concludes that it represents a - — warm water assemblage of Indo Pa c ific affinities . He has recog n ize d four members in the formation . The lowermost member is characterized by dark fin e-grained shales and sandstones which contain a fauna provisionally referred by him to th e n o nfo il Horsetown . The three other members consist of s s if er ous conglomerates and an intermediate shale series . Only th e o two shale members have yielded fossils at Mitchell , but a Chic fauna comprising m a ri n e ~ i nverte b rates has been found not f a r

n . away at Antone , i conglomeratic sandstone On a hill above Mitchell a small flora made up largely of cycads has been re c ferred provisionally to the Upper Creta eous by the writer . The withdrawal of the Cretaceous seas incidental to the Lar amide revolution brought the marine history of eastern Oregon to an end . It is possible that a minor uplift along the axis of the Cascade Range served as a barrier to the eastward advanc e of the Tertiary seas , but it can not be considered to have been high enough to form a climatic barrier . — E ocene . There is no depositional record for the early part of d the Eocene epoch , but from the Willamette Valley westwar there are widespread deposits of middle and upper Eocene age . - These comprise marine sediments of a shallow water type, con taining abundant marine invertebrates , and terrestrial deposits ,

f . largely tu faceous , containing many fossil plants The Clarno formation to the east of the Cascade Range is largely volcanic , tufl s with rhyolitic and andesitic flows and intrusions , also and agglomerates which are exposed along the John Day River near ’ l a rn o s ufl C Ferry . Leaf impressions in the finer t s and shale s at several localities indicate the middle Eocene age of at least that portion of the formation ; but there is some reason to b e lieve that the volcanic activity which gave rise to the Clarno formation continued into the Oligocene , because near Fossil an

Oligocene flora occurs in beds referred to the Clarno . A flora of 20 middle or early upper Eocene age from Comstock , about 10905 8—3 2—2 6 $ V I INTERNATIONAL GE O LOGI CAL C O NGRESS

3 2 miles ( kilometers) south of Eugene, has been studied by Dr .

. S Ethel I anborn, of the University of Oregon , who relates it to similar Eocene flo ra s in southern Oregon and northern California and to the Clarno flora of eastern Oregon . This Comstock flora and a flora of upper Eocene or lower Oligocene age from Goshen , 7 miles southeast of Eugene , both indicate a u warm temperat re and proximity to the sea . The Goshen flora has its modern equivalents in Mexico and Central America , with - d efin e d flo ra s a well Asiatic element , and is more like the Eocene of the southeastern United S tates than any other now known in western America . The Clarno flora is characterized by genera whose modern equivalents req uire a more temperate climate than those of the Goshen but which indicate a warmer, more humid climate than that of the John Day and later epochs . - Oli ocen e . b e g As indicated above , there is some reason for lieving that the Clarno volcanic activity was more or less contin n ous in eastern Oregon during Oligocene time , as marine deposits containing an Oligocene invertebrate fauna in the Willamette f Valley and in the Coast Range, to the west , are largely tu faceous . The John Day formation which rests unconformably upon the Clarno in the John Day Basin and elsewhere in eastern

Oregon , has been considered to be Oligocene on the basis of its mammalian faunas but S tock (25) considers these to rep resent a distinct advance over the faunas of the Oligocene White River of the Great Plains and to be more nearly related to the S lower Rosebud fauna of outh Dakota , of upper Oligocene or lower Miocene age . Among the common genera represented are

P a ra cot l o r E oreodon Gom hotheri um Di cera theri urn . y p , p , p , and

The extensive fossil plants of the Bridge Creek flora , from the flo ra s lower John Day formation , closely resemble Miocene from various parts of western America . The John Day formation will therefore be considered under the Miocene , with the reser vation that it may be in part of upper Oligocene age . Prior to the John Day epoch the Clarno rocks were slightly folded and widely eroded . — M ee i o ne . With the deposition of the John Day formation at the end of the Oligocene and the beginning of the Miocene , volcanic activity, though continuing , became subordinate to gradational processes . Most of the sediments making up this formation are of volcanic origin , and some of the ashy shales bearing fossil leaves contain pumiceous fragments which have 1 8 been transported only a short distance . Merriam ( ) has di — vid e d the series i nto three parts a lower division m which red d ish shale predominates and breaks down to form characteristic mu d-covered domes ; a middle division m which gray to gray e tu fl s gre n and shales are conspicuous , commonly exposed as s teep pinnacled cliffs , and an upper division characterized by CENTRAL OREGO N 7

b uff tufl a ceo us and ashy deposits . In the lower division occurs the extensive Bridge Creek flora in which S equoi a and its asso ciates are represented . Few fossil plants occur in the middle and upper divisions , and these are not greatly unlike the Bridge vi m a m Creek flora . The middle and upper di sions contain a 100 malian fauna of more than species , among which members of ’ the Oreoa on group are most Characteristic . Except for the a p e a ra n c e P romer eockoerur p in the upper division of the genus y , there is little basis for distinguishing the faunas of the middle and upper divisions . S e uoi a The occurrence of fossil q , together with the Tertiary equivalents of most of the modern associates of the redwood , i n o t ' un lik e ndicates valley habitats , with a climate that of - to day along the coast of the northern half of California . This 40 climate , characterized by an annual rainfall of more than i inches meters) and by m ld , equable temperatures , appears to have extended north into Alaska and across to S iberia and M flo ra s anchuria , where similar of presumably the same age have been recognized . The mammalian fauna of the middle and upper parts of the John Day formation indicate well-watered o pen country .

The Eagle Creek formation , which is exposed in the gorge of the Columbia River west of the Cascade Locks , is probably the equivalent of the upper John Day and contains a flora that has some elements in common with both the Bridge Creek and the M ascall fl o ra s ; in its lack of the S equoi a element it indicates less humid conditions than those of the typical lower John Day formation (Bridge Creek) of the John Day Basin .

The dominantly basaltic Columbia River lavas , resting on the eroded surface of the John Day formation , comprise more 25 ufl t . than flows of olivine basalt , with intercalated and gravel S This formation formerly covered much of the tate of Oregon , f orming the great i nterior plateau and possibly most of the

$ Cascade Range ; it extends northward into Washington , east ward into Idaho , and southward into California . Temporary conditions suitable for the growth of forests may be noted in scattered intercalated sediments , of which those exposed along the Columbia River Highway north of The Dalles and containing i the rema ns of large trees show the best development . i c After local eros on of the Columbia River lavas , these rup - tions gave way to showers of light colored ash , some of which accumulated I n lakes and river valleys and with some sand and conglomerate make up the Mascall formation . This formation is especially well developed near the Mascall ranch , below Day ville 0 1 . (station , pl The vertebrate fauna includes among M er chi ur i ron erur Ni ola bi r tra ns its representative mammals y pp , m on ta n ur P a ra hi ur A rcheohi ur D romomer x Te hroc on , pp , pp , y , p y , 8 $ V I INTERNATIONAL GE O LOGICAL CONGRESS

hi c on Le ta retur . Amp y , and p A progressive trend toward aridity S e uoi a is indicated by the Mascall flora , in which q and its asso ciates are no longer dominant , the oaks and other characteristic species have their modern equivalents 1 n the California Coast 1 s 3 0 Ranges , where the annual rainfall not more than inches meter) and Where the temperature is more variable than

b elt . in the redwood , to the north This trend toward aridity , which has continued down to the present time , may be largely attributed to the climatic barrier formed by the rising of the

Cascade Range to the west . The correlative of the Mascall in eastern Oregon and Idaho is the Payette formation . Faunas most nearly related in stage of evolution are those from the Pawnee Creek of Colorado , the N lower Snake Creek beds of ebraska , the Madison Valley of M er chi u; Montana , and the y pp zone of the north Coalinga region in California . The essential homogeneity of this faunal stage over so broad an area during middle Miocene time is noteworthy . — P li ocen e . The Rattlesnake formation is made up of rhyolitic

f . flows and plugs , with associated gravel and tu f It rests upon the Mascall with a well-marked s tructural unconformity at the type locality at the upper end of Picture Gorge , near Dayville (locality and its uppermost rhyolite flow forms a distinct capping wherever the formation has been noted . The fauna 1 s Neohi a ri on P li o regarded as lower Pliocene and includes pp , leocera r I n da rctor ore on enri r S hen h lor hi ur Te o a . pp , , g , and p p It is closely related to that of the Thousand Creek beds of Nevada and is later than that of the Ricardo deposits of the Mohave

Desert , California . The Clarendon fauna of Texas is nearly No related . fossil plants are known from the Pliocene of Oregon , but the floras of that age in California indicate increased aridity , 1 s which consistent with the character of the mammalian fauna . The andesites of the Cascade Range may be 1 n part of Pliocene age , but for the most part they appear to be younger and are described under the Pleistocene . The great diastrophic events that resulted I n the formation a l of the Cascade Range , the Blue Mountains , and possibly so the Oc ho co Mou ntains had their inception late in the Miocene or early in the Pliocene . The Rattlesnake formation is only to a small extent involved in the folding in the Crooked River and

John Day Basins . Folding and faulting appear to have con ti nued through much of the Pliocene and I n more easterly parts of Oregon are still going on , and the volcanic activity associated with these movements has continued with minor cessations down to the present time . In the Cascade Range the Pliocene i sxrep re s en ted by large wh 1 ch i a mounts of volcanic rocks , $range in compos tion from

10 xv1 INTERNATIONAL GEOLOGICA L CONGR ES S given by the greater part of eastern Oregon is that it is carved from nearly horizontal lavas .

ITINERAR$

The excursion starts at Eugene , Oregon . At Skinners Butte is exposed a sheet of Columbia River ’ tufl s lava overlying the Oligocene , and marine sediments and dipping eastward toward the Cascade Range . From the top a there is general view of the Coast Range , the Willamette

Valley , and the Cascade Mountains . Honeysuckle and Gillespie Buttes are capped by river gravel and indicate the former high level of the Willamette River . M c Kenzi e The route leads eastward over the Highway , fol x n ie lowing to a considerable e tent the Mc Ke z River . Here may be seen the river terraces a nd the eastward dip of the f basaltic lavas and tu fs . Between Walterville and Vida the basaltic lavas that occu r along the western margin of the Cascade Range grade through a series of agglomerates and tuffs into the normal andesite s characteristic of the main mass of the range between Vida a nd

Belknap Springs . This part of the range includes andesites O (variously characterized by Iabradorite , andesine , and ligo

ff . clase) , rhyolites , tu s , and agglomerates

2 . At Indian Creek and at Nimrod are small masses of diorite and granodiorite which intrude the andesites of the main mas s of the range . Four miles kilometers) north of the Blue River is the 1 70 000 Blue River mining district , which produced $ , in gold and silver from the oxidized portions of veins of quartz a nd brecciated country rock containing sphalerite , galena , chal

CO rite . i py , and pyrite This associat on is characteristic of sev eral such mineralized areas along the central axis of the range . ie 3 . At Mc Kenz Bridge is the end of a tongue of flows of gray olivine basalt which projects westward from the mass of the younger Cascade Range to the east , and which lies between the

M c Ken ie . s z River and Horse Creek , to the south These lava are strikingly unconformable with the high range of andesites to the west . Here also is the broad valley flat of glacial outwash . The uneven morainal surface may be noted 4 miles kilo meters) east of M c Kenzi e Bridge . 4 . At the road forks to Belknap Springs (hot springs issuing from agglomerate of the older series) the glaciated valley of 1 Lost Creek s entered . One mile kilometers) up the valley

N 1 umbers refer to points so indicated on Plate . CENTRAL OREGON I I is the terminus of a postglacial lava flow which occupies th e bottom of the valley .

5 . At Deadhorse grade , at the head of the Lost Creek Valley , can be seen the lava flows that tumbled over the steep valley fl of wall . Also from this point is visible to the west the tongue younger lavas projecting down the old M c Kenzie Valley a nd the steep east front of the older Cascade Range . flow 6 . The crater and lavas of the Recent Belknap lava

l . 2 A . (p , ) lie near the highway

M c Ken ie s . z Pass , at the summit of the Cascade Range , give B S . S ee . 2 . a view of the Three isters and other peaks ( pl , )

From this point the character of the vegetation changes , first to pines and then to junipers and sagebrush . The highway M c Kenzie follows the lava flow , lying in a valley cut in the ande l a cio site surface . This surface is extensively covered by a g vi a ile flu t mantle .

On the road from the town of Three S isters to Bend there is . evidence that the andesites of the Cascade Range overlie the in Pleistocene Madras formation . On the Madras Plain and the valley of the Deschutes River the Madras formation is shown - h to be made up of torrent laid material of volcanic origin , wit associated lava flows .

7 . ff to Pilot Butte , a Recent volcanic peak , a ords from the p Oc ho co a view of the Cascade Range , to the west , and the and

Paulina Mountains , to the east and south . From Bend the highway leads northward to Redmond and the eastward over the Madras Plain . On the Madras rim , above town of Prineville, may be seen the structure of the Columbia .

River lava on the south side of the Oc ho co Mountains . From Prineville eastward and northward over the Oc ho co

Highway to Mitchell the road follows the Ocho co Valley and . d Ocho . a n crosses the co Mountains A forest of pine, with fir La rix larch ( ) at the higher levels , obscures most of the geology, but at several points the Clarno formation may be noted . This . formation diff ers from the Columbia River lava in being made up largely of fragmental and explosive volcanic products , with

m a l , flows and intrusive bodies of relatively s l extent . It also e contains much rhyolite and andesite rather than basalt . Th upfolding of the Oc ho co Mountains in an asymmetric anticline with its steepest clips to the north has caused the removal of the Miocene and Oligocene lavas and tuff s and the exposure of the - Eocene Clarno, with its bright colored badlands and pinnacle topography . On the descent of the north slope the badland topography of the John Day Basin may be seen to the north , with a capping lava of Columbia River on the higher buttes and ridges . Jus t 1 2 $ V I INT ERNATIONAL GEOLOGICAL C O NGRES S

b elow the ranger station Cretaceous conglomerates crop out

on the left side of the highway, representing part of a strip ex 1 5 24 tending for some miles ( kilometers) , to Mitchell and

beyond , with a thickness of several thousand feet . The un c onformity between the Clarno and the underlying Chico is

s . triking The highway reenters the Clarno formation , which

extends down nearly to the covered bridge at Bridge Creek, - b elow Mitchell . This formation contains a well developed Ara li a Ci n n a momum flora , in which , , and other typical

Eocene genera are represented . The best locality for collecting ff i s a short distance o the road . The contrast between the warm

temperature Clarno flora , with species related to those now - living in low latitudes , and the typically temperate climate Bridge midd e l 8 . Creek flora , of Tertiary age, will be noted at stop Near the covered bridge the road crosses the Clarno-Chico

contact , and from this point into Mitchell the Cretaceous sec - tion is well exposed along the axis of a pre Clarno fold .

For most of the distance east and south toward Dayville , the r oad runs along the strike of the Clarno formation , with Rattle

snake rhyolite and gravel capping the ridge to the north . In the

9 . canyon of Rock Creek ( , pl 1) the Miocene Mascall formation

overlies the Columbia River lava , and the road enters a narrow g orge in the basalt which extends to the John Day River and

' e Picture Gorge . To th e a s t the Mascall formation is exten ivel s 10 . y exposed in the vicinity of the Mascall ranch ( , pl and from this point can be seen the southward-dipping Columbia

River lava , on which lies the Mascall formation , without angular

unconformity, with a capping of nearly horizontal Rattlesnake B . S ee . 3 . rhyolite ( pl , )

The type locality of these formations , from which most of the vertebrate material studied by Merriam and S tock has been

c . ollected , lies between the Mascall ranch and Picture Gorge Picture Gorge is the narrowed valley of the John Day River

where it crosses the Columbia River lava . The unconformable contact of the Columbia River lava on the John Day formation may be seen at S heep Rock

Where a small mass of basalt caps the summit . A few miles to the north and up the dip conspicuous cliffs of Cretaceous con

glomerate are terminated by a fault . The John Day beds

. 3 A ( pl , ) with overlying basalts of Columbia River lava occupy 25 40 the valley over a distance of about miles ( kilometers) . The Davis dikes intrude the John Day beds for a distance of At several miles along the valley . several points along the

road a layer of Recent ash may be seen covered by alluvium . S Beyond ervice Creek the route crosses the Grizzly fold , and CENTRAL OREGON PLATE 2

BE K E A . L NAP CRAT R

Near the summit of the Cascade Range . From this vent have issued almost within x historic times the black olivine basalts e posed on the slopes of the cone .

$ B . V I EW FROM M C KEN I E HIGHWA$ N EAR THE SUMMIT

i n North and Middle Sister Peaks in the background ; recent basalt the foreground . 1 2 $ V I I NT ERNATIONAL GEOLOGICAL ON G R E S S

' below the ranger station Cretaceous co n g m e ra te s crop out re re s e nti n p a rt 1 ex on the left side of the highway , p g of a str p tending for some 1 5 miles (24 kilometers) to Mitchell and

tho u s 1 d . un beyond , with a thickness of several feet The c onformity between the Clarno and the ud e rlyi ng Chico is Cla rno f o rm a tio n s triking . The highway reenters the , which b rid ca t extends down nearly to the covered g Bridge Creek ,

s - below Mitchell . This formation contain a well developed A ra li a Ci n n a momum a d t flora , in which , , other ypical lit o Eocene genera are represented . The best l oa y for c llecting e w e is a short distance O ff the road . The co ntra s o t e n the warm re ee d temperature Clarno flora , with species l to those now te m ea te- living in low latitudes , and the typically p climate Bridge d r nte o 8 . Creek flora , of middle Tertia y age , will be at st p Near the covered bridge the road c ro s s esthe Clarn o-Chico te s ec contact , and from this point into Mitchell Cretaceous — tion is well exposed along the a xis of a pre (a rno fold . a s twa rd For most of the distance e st and outh Dayville, the fo rmtio n w road runs along the strike of the Clarno , ith Rattle

snake rhyolite and gravel capping the ridge tct he north . In the M io c e nd\/Ia s c a ll n 9 . 1 canyon of Rock Creek ( , pl ) the formatio red overlies the Colu mbia River lava , and the enters a narro g orge in the basalt which extends to the Je n Day River a n a i e x f Picture Gorge . To the east the Mascall frm t o n is t s ivel r 0 a 1 . y exposed in the vicinity of the Mascall ch ( , pl from this point can be seen the s o uthwa rdi ipp i n g Colu m fo rm a tin River lava , on which lies the Mascall , without ang ho rio n ta l R a ttl e s r unconformity , with a capping of nearly

B . . 3 . S ee rhyolite ( pl , ) 5 1 m m c The type locality of these formations , which the vertebrate material studied by Merriam n d S tock ha c a d ollected , lies between the Mascall ranch Picture Picture Gorge is the narrowed valley of 1 1: John Day v where it crosses the Columbia River la a . The unconformable contact of the COIL the John Day formation may be seen a where a small mass of basalt caps the s um the north and up the dip conspicuous cliuf glomerate are terminated

. 3 A (pl , ) with overlying b a

The Davis dikes i ntrud several miles along t road a layer of Re CENTRAL URI PI

BE K ' ' v1 . L NAP CR AI E R

Ne a r t he summit of the (I s ee de Range . F historic time s the W ine basalts

vol . 7 e Sisters

: gon Geol . Soc .

J re o n . g Univ Pub .

John Day B as 1n i of the John

1906 . DA$ E$ E DA$ $ 1 5 A . JOHN FORMATION POS D ON JOHN HIGHWA MILE S B ELOW DA$ V I LLE

Showing a rhyolite flo w in green a n d buff tuff s . Photograph by R . W . Chaney .

E E E C C B . V I WS NORTHW ST FROM TH MAS ALL RAN H

Sh o wi n g the s tee pl y dippi n g Co lumbi a Rive r lava s a n d light -colored Mascall tuff s

o ve rl a i n by th e m o re n e a rly hori zo n t a l R a ttle s n a ke rhyolite . Photograph by

. C a n e . R \V . h y

I 4 $ V I INTERNATIONAL GEOLOGICAL C O NGRESS

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