State of Washington

DANIEL J. EVANS, Governor

Department of Conservation H. MAURICE AHLQUIST, Director

DIVISION OF MINES AND GEOLOGY MARSHALL T. HUNTTING, Supervisor

Geologic Map GM-3

GEOLOGY OF THE

SIMCOE MOUNTAINS VOLCANIC AREA,

WASHINGTON

By

RICHARD A. SHEPPARD

STATE PRINTING PLANT, OLYMPIA, WASH.

1967

For sale by Department of Conservation, Olympia, Washington. Price, $1.00

WASHINGTON DEPARTMENT OF CONSERVATION DIVISION OF MINES AND GEOLOGY

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Approximate mean declination,

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Bose from Army Map Service Topograp hic

Quadrangles, Yakima and The

Dalles, 1,250,000

2 3 4 5

SCALE

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1957

6 Miles

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R I E R 16 120°45' R I E

GEOLOGY OF THE

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Geology mapped 1958-59

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Area mapped

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EXPLANATION

Oo

Andesi te of Mount Adams

lntroconyon flow , light- to dark-grey; vpper vesicular

port g rades downward throuJh platy zone lo columnar

jointed lower part; hyn lnpi liti~ nntJ rvotphy , ille; cc,n­

tai ns o,cillatory :z;onod plogioclose (An50

_28

), clino­

pyroxene (+2V,,,51°-49°), end hyper<thene (-21/=64°

-60Q), ond rare oliv ine phenocry,t, in groundmo,s of

plogiodose (An32_2gl , clinopyroxene (+2V"'13°-4°),

opaque minerol,, ond pink to p<lle - brown glo,s . Prob­

ab ly e xtruded from the ;oul,,.,o,f flank of Mount Adorn,

Contact

Dashed where approximate

Li ~-,c~~~-~ .•••.

D

Fault

Dashed where approximate; dotted

where concea led; U, upthrown

side; D, downthrown side

Anticl ine

GEOLOGIC MAP GM-3

Showing trace of axial plane. Dashed

where approximate; dotted where

concealed.

Syn cl ine

Index map of Washington showing area mopped

Qb

Ol ivine basalt of King Mountain

Showing trace of axial plane and pl unge

of axis, Dashed where approximate;

dotted where concea led

Olivine basalt of the Simcoe Mountains

QT b, flows, groy, 3 to 40 fee t thick; inter­

granular to diktytowi lic, gene ra lly non­

p;;rphy ritic but contoin os much as 15

percent plagioc lme (A n56

_43J and olivine

(Fo81 _60

) phenocrysts in nearly ho lo ­

cryoto lline groundmos, of plogiocla,e

(An 49 _40

), clinopyroxene (+2V=S6°- 45°),

o livine (Fo65

_40

) , opaque mio,;,ml,, ,:,nd

apatite; gloss content genera lly le;, than

2 percent; olivine phenoc rysts commonly

re,orbed and portly a ltere d lo idd ingsitc;

rore quartz xenocry,t, ,urrounded by

clinopyroxene reoction rim; vesic le,

locally lined with calcite ond (or) hyo­

lite. httuded from northwest - trending

wne of shield vokonoe, ond loco I vents

OTbs, ;coria cone,; generally 150 to

JOO feet high; mainly red to dork-grey,

poorly <0rted, gen,arcl ly umcnn«:, li doted,

itratified scorio; ,ome ,pindle-shoped

bom~. Mony in southern port of oreo

alignd olong northwest-trending Hnes,

,uggesting fou lt contro l. Moy ba: os

young cs Recent

FEET

6000

5000

4000

~000

tOOO

B

~ O livine basalt of Lincoln Plateau

Flow,, groy , generclly 10 to 20 feet thick;

holocry,tol line, intergn:mvl<>r to dikty­

taxitic, ond porphyritic; conta in o livine

{fo80_65) phenocryits in groundmcs, of

plog ioclase (An 48_40

), clinop~roxene

(+2Va. S4° -50°), o liv ine (Fo60

), opaque

mineral,, end ap;;tjte; glorneroporphyr iti c

clot> of o livine pl,~,,u~ry,t, common~

olivine phenocrysts commonly resorbed

and portly oltered lo iddingsite. Erupted

from o shield volcano on Lincoln Ploteou,

north of oreo

UNCONFORMITY

EI lemburg Formation

Moinly grovel ond mnd of fluviol or igin , light-yellow

to ye llowi,h-brown, poor ly sorted, poorly consolidated;

,and, fine- to coorse-gr<>ined, micoceous, loca ll y

crossbedded; grove l consist; mostly o f rounded pebble,

ond cobbles of GSortzjte in micoceou; sond ma trix;

grovel, in upper pa rt of format ion between Bowmen ond

Canyon Creeks locolly consist mostly of greenish-gray

and light-pu rpl e porphyritic docite. Top of formation

eroded, moximum expmed thickness 250 feet

Yakima Basal t Flow,, block but weather brown to brownish groy,

generally 70 to 150 feet thick; locol interloyen of

diotomite and tu llcceou, sond;tone; two - t ier jointing;

upper port ve,icu lcr grading upward to ocori oceou, top;

intersertal and generolly nonporphyritic; contoln plo­

gioclo,e (An50

J, clinopyroxene (+2V=44°-38°) , opaque

mineral,, ond l;ttl<> or no olivine (Fo80

); g loss c<>nlenl

10 to 30 p,arcent, lc,col ly cho rged with c lino pyroxene 1

opaque minerol;, end opotjte; ch lorophoeite or its

olterotion product, generolly fil l interst ices. Bose of

forma tion not exposed, toto l thickn•" unknown

OT" 0Tb

• •

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-

lnt-coconyon flow<, g,oy, g,aMro lly 10 lo 1S f,a,al th; ck;

holocry,tolline, diktytoxitic, end porphyritic; contain

p log ioc lose (An58

_50

) ond olivine (Fo78_60

) ph~no­

crysts in groundmos1 of plog;oclose (An50_46), ophltic

to ,ubophitic cl inopyroxene (+2V:54°-52°), olivine

{Fo55

), end opoque minerol,; glomeroporphyritic

o li v ine common. Extruded from King /V\ountain, o

shield volcano southeast of Mount Adams in T. 7 N .

R. 11 E.

Pyroxene -olivine basalt

O Tp, Flows, grey, 20 to JO feet thick, holo•

crystalline, intergronulor to pilotaxitic,

and porphyritic; contain plogioclase

(An58_38>, olivine (Fo81 _60

), clinc­

pyroxene (+2V~56°-49°), and rare

hypersthene pheoocrysts in g roundmcs;

of pl agloclase (An46_36), clinopyroxene

(+2V--54° - 49°), f,oceifo rou , olivine, and

opoque mineral,; hypersthene resorbed

and surrounded by granulor c linopyroxene.

Erupted from locol vent,

QTp,, ,coda cones; mo;n ly red to dork•groy,

poorly sorted generally uncon<0 lidoted,

stratified ,corio; contains p log i oclose,

olivine, and dinopyroxene phenocr)·st,.

May be os young o; Recent

Andesite of Signal Peak

Flows, dork-g roy, 10 to 30 feet thick; in ter~

sertal ond porphyritic; contain oscillotay

zoned plog;oclo;e (An50

_32J, olivine

(Fo70

_50

), hypersthene (-2V=55°-50°),

ond clinopyroxene (+2V=50°) phenocrysh

in groundmoss of p lagioclase (An36

_28)' clinapyroxene (pigeoni1e and augi te) ,

<>f><'<tUO minoro,ls, <>poli te , ond pola - b,own

gloss; gloss content generally 10 to 20

percent; reaction rims of cl ;nopy roxen e

surround o livine and hypersthene pheno­

cry,ts; glomeroporp~yritic plogioc lo ;e

common. Extruded from Slgnol Peak,

o steep-sided volcono in sec . 36, T. 'l

N. , R. 13 E.

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Str ike and dip of beds and flows

• Horizontal flows

QTd

Dacite Domes, light- lo da,k-g r<>y, poorly exposed;

flow bonded, hyo lapi li tlc, and p;;rphyri tic;

con~in o,cillotory zoned plagioclase

{An44

_27

), olivine (Fo46

}, cllnopyroxene

(+2V=Sl 0 -48°), hypersthene (-2V=72°

- 53') , oxyhornblende , biotite, ond rare

son idine phenocrysts in groundmoss o f

i,lo~ioclase {An30

_26

), c linopyraxene

(pigeonite(?)), opoque mine ra l,, end

pole-brown gloss; olivine ond hyperuhene

rimmed by granular dinopyroxene;

oxyhornb lende and biotite rlmmed or

entire ly reploced by opcGue minernls;

gloss content generally 30 lo 50 p,,,c.,nl

OTr

Rhyoli te

Flows on~ dome (?}; white to dor k-grey,

poo r ly exp;;sed; flow bonded and spheru­

litic; ge nera I ly conh:Jin less than J per­

cent plogioc lo,e (An22

_18

), sanid ine,

quart•, ond clinopyroxene (+2\1"'55°-53°)

phenccrysts in glossy matr ix conta ining

obundont flow- a ligned cr)'Slol lites;

rcfradive ind~x <>f g lco» r~,-,ge , fr<>m

l.501to 1 .4'12. Eruptedfrom loca l

vents in central and eost-centrol ports

of m eo

SUMMARY

The o ldest formation exposed in the oreo is the Yo kimo aci,olt of Miocene end Pli<>cene age . This vo,t Pyroxene -oliv ine bo,o lt and rhyolite ore contemporoneous with the olivine booolt, but ondesite of Signol

ier ies of plateau boso lt, covers o lorge portion of eo;tern Wo,hingtoo , northeo,tern Oregon, ond northwe,tern Peok and docile probably postdote oll of the boso lt except thot of the poro,itic scorio cones. The building of

Idaho. Fo l lowing th e extrusion of the Yokimo Boso It, quartzite -bear ing grovel, of the EI lensburg Fo,motion

were deposited by southwestward flowing ,trecms. North of the mopped creo, the GUOrtzite - beoring grovel,

were s•,cceeded by o thick occumulotion of rhyodocit ic or onde,it ic debris thot ,•,os ,tream-tro n,p;;rted from

volcanic centers in the Co,code Mounta;ns (Wcters, 1961, p. 53-Sj).

The east-we,t antic I ina I ridge, ,uch o, Peovine -Toppen ish Ridge ond the Hone Heaven Hi 11, re,u lted

from o reg iono l deformation contemporaneous with deposition of the upper port of the Ellensburg Formation

(Waters, 1955, p. 674-675). Eroi ion ;ub,equent ly removed mo;! of the Ell ensburg Fornu li on from the onti­

cline, prior to the erupt ion of oliv ine bosalt of the Simcoe Mounta ins.

There appears to be little regul ar ity ;n the sequence of eruption of the vor ioL1s ro ck type, in the Simcoe

Mountoin, volcon ic oreo. Olivine boso ll wo, erupted th1ough0ut l~.e vo lcanic history . Much of the olivine

basalt wos erupted from o northwest-trending li ne of 1hield volcanoes between the westword extension of the

Horse Heoven Hil li ond Toppenish Ridge and become loco lized in t~e synclinol vol ley between the two r idges.

Olivinre bc,olt c l,o wa, ~rupted contemporaneously from o low ,hie ld volcano on the Lincoln Ploteou north of

the mapped area .

'"

FEET

,000

•OOO

aooo

A

' ' ~ • • 2 Qo 2000•-j--;;;:--- ' / . Qb "V"/ ,000

' -' " , '

numerous basa ltic ,cario cones marked the clos ing phase of volcon i,m. Many of the cones, po rticu lcrly those

in the southern eort of the oreo, show o linear arrangement, suggesting foult cont,ol.

lntrocanyon flow, of olivine basa lt fram King Mountain , a shield volcano southeast of Mount Adam,,

flowed down the Klickitat Conyon bi.it wer,a lote, eroded ~ut by th,a Klickitat River, A single intr~conyon

ondes ite flow from Mount Adorns then portia lly fi l led the new conyon.

The re is no direct evidence t<> indicate that glacier< eve r occupied any port of the Simcoe Mountains;

however, both So tus Creek ond Devi ls Conyon head in omphitheoters. Possi bly , small alpine glac iers once

occupied these amphitheaters.

REFEREN CE S

Woters, A. C., 1955, Geomorphology of ,outh-centrol Wa,h ington, i llu,troted by the Yokima Eo,t Guod rongle ;

Geol. Soc. Americo Bu ll., v. 66, p . 663-684.

OAK HIU

-~QTbs

-----, 1961, Keechelu, problem, Co,ccde Mou nto ins, Washi ngton; Northw.ast Sci,, v, 35, p. 39-57.

A' A"

POAVIIIE RLOG€

on

GEOLOGIC SECTION A LONG LINE A-A'-A"

' ' 0 • ' • B'

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::: ==.........: = --= ------,,---- -- - ~ - == == ==-~ __:=.- - --_...,/ / :-:----; r-=:--:: ==- -==-== =--- -==-.:::.:::::: == ==~ ----------- - - - - -----_:::-____ ·-i---=:------ -·.-= ==----~-----==-- / ...... ....__ .................. -----...::-----------=----- ---==- ------- - ---__ -'--- "'"' -~"°'~------==-==-==-==-c.._J _______ =-==C::----===:_--""''-..<~--"'--'-=--'c-=---=-===----'"-==~--- ---=:c-=------==-==-==-====-==-=='-'==-==-=-----L SOIi l EV£l-

GEOLOGIC SECTION ALONG LINE B-B'

For sa le by Department of Conservation, O lympia , Wash.

SIMCOE MOUNTAINS VOLCANIC AREA, WASHINGTON Price $1 .00

By Richard A. Sheppard

1967