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 GEOLOGIC MAP DIVISION OF MINES AND GEOLOGY GM-3
- _, E R 6 E i:; ,. E EXPLANATION
Oo T q / T 9 "'I H', 1 ·I Andesi te of Mount Adams ' lntroconyon flow , light- to dark-grey; vpper vesicular Contact port grades downward throuJh platy zone lo columnar Anticl ine jointed lower part; hyn lnpi liti~ nntJ rvotphy , ille; cc,n Dashed where approximate tai ns o,cillatory :z;onod plogioclose (An _ ), clino 50 28 Showing trace of axial plane. Dashed pyroxene (+2V,,,51°-49°), end hyper
l QTd OTr Ty ~ Olivine basalt of the Simcoe Mountains O livine basalt of Lincoln Plateau Pyroxene-olivine basalt Andesite of Signal Peak Dacite Rhyoli te
\ QT b, flows, groy, 3 to 40 fee t thick; inter Fl ow,, groy , generclly 10 to 20 feet thick; O Tp, Flows, grey, 20 to JO feet thick, holo• Flows , dork-groy, 10 to 30 feet thick; in ter~ Domes, light- lo da,k-g r<> y, poorly exposed; Flows on~ dome (?}; white to dork-grey, T ' granular to diktytowi lic, genera lly non holocry,tolline, intergn:mvl<>r to dikty crystalline, intergronulor to pilotaxitic, sertal ond porphyritic; contain oscillotay flow bonded, hyolapi li tlc, and p;;rphyri tic; poo r ly exp;;sed; flow bonded and spheru p;;rphy ritic but contoin os much as 15 and porphyritic; contain plogioclase zoned plog;oclo;e (An _ J, olivine con~in o,cillotory zoned plagioclase litic; genera I ly conh:Jin less than J per taxitic, ond porphyritic; conta in olivine 50 32 (An _ >, olivine (Fo _ ), clinc (Fo _ ), hypersthene (-2V=55°-50°), {An _ ), olivine (Fo }, cllnopyroxene cent plogioc lo,e (An _ ), sanidine, percent plagioclme (A n _ J and olivine {fo _ ) phenocryits in groundmcs, of 58 38 81 60 50 44 27 46 56 43 80 65 70 0 22 18 (Fo _ ) phenocrysts in nearly ho lo plogioclase (An _ ), clinop~roxene pyroxene (+2V~56°-49°), and rare ond clinopyroxene (+2V=50°) phenocrysh (+2V=Sl -48°), hypersthene (-2V=72° quart•, ond clinopyroxene (+2\1"'55°-53°) w 81 60 48 40 C cryotolline groundmos, of plogiocla,e (+2Va. S4° -50°), o livine (Fo ), opaque hypersthene pheoocrysts in groundmcs; in groundmoss of plagioclase (An3 _28)' - 53'), oxyhornblende, biotite, ond rare phenccrysts in glossy matrix containing © 60 6 u (An _ ), clinopyroxene (+2V=S6°- 45°), of pl agloclase (An _ ), clinopyroxene clinapyroxene (pigeoni1e and augi te), sonidi ne phenocrysts in groundmoss of obundont flow- a ligned cr)'Slol lites; 0 49 40 mineral,, end ap;;tjte; glorneroporphyritic 46 36 o livine (Fo _ ) , opaque mio,;,ml,, ,:,nd (+2V--54° - 49°), f,oceifo rou , olivine, and <>f><'
young cs Recent EI lemburg Formation 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 in e bo,o lt and rhyolite ore contemporoneous with the olivine booolt, but ondesite of Signol Moinly grovel ond mnd of fluviol origin, light-yellow ieries 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 bosolt except thot of the poro,itic scorio cones. The building of w C to ye llowi,h-brown, poorly sorted, poorly consolidated; Idaho. Fo l lowing th e extrusion of the Yokimo Boso It, quartzite-bearing grovel, of the EI lensburg Fo,motion numerous basa ltic ,cario cones marked the clos ing phase of volcon i,m. Many of the cones, po rticu lcrly those © u ,and, fine- to coorse-gr<>ined, micoceous, locally were deposited by southwestward flowing ,trecms. North of the mopped creo, the GUOrtzite - beoring grovel, in the southern eort of the oreo, show o lin ear arrangement, suggesting foult cont,ol. 0 crossbedded; grove l consist; mostly of rounded pebble, were s•,cceeded by o thick occumulotion of rhyodocit ic or onde,itic debris thot ,•,os ,tream-tro n,p;;rted from a: ond cobbles of GSortzjte in micoceou; sond ma trix; volcanic centers in the Co,code Mounta;ns (Wcters, 1961, p. 53-Sj). lntrocanyon flow, of olivine basa lt fram King Mountain , a shield volcano southeast of Mount Ad am,, grovel, in upper part of formation between Bowmen ond flowed down the Klickitat Conyon bi.it wer,a lote, eroded ~ut by th,a Klickitat River, A single intr~conyon Canyon Creeks locolly consist mostly of greenish-gray The east-we,t antic I ina I ridge, ,uch o, Peovine -Toppenish Ridge ond the Hone Heaven Hi 11, re,u lted ondesite flow from Mount Adorns then portia lly fi l led the new conyon. and light-purpl e porphyritic docite. Top of formation from o reg iono l deformation contemporaneous with deposition of the upper port of the Ellensburg Formation eroded, moximum expmed thickness 250 feet (Waters, 1955, p. 674-675). Eroiion ;ub,equently removed mo;! of the Ell ensburg Fornuli on from the onti There is no direct evidence t<> indicate that glacier< ever occupied any port of the Simcoe Mountains; cline, prior to the eruption of oliv in e bosalt of the Simcoe Mounta in s. however, both So tus Creek ond Devi ls Conyon head in omphitheoters. Possi bly, small alpine glaciers once occupied these amphitheaters. There appears to be little regular ity ;n the sequence of eruption of the vorioL1s ro ck type, in the Simcoe Mountoin, volconic oreo. Olivine bosoll wo, erupted th1ough0ut l~.e volcanic history . Much of the olivine REFEREN CE S 1 5 ~ T 5 N basalt wos erupted from o northwest-trending li ne of 1hield volcanoes between the westword extension of the Woters, A. C., 1955, Geomorphology of ,outh-centrol Wa,hington, i llu,troted by the Yokima Eo,t Guod rongle ; Horse Heoven Hil li ond Toppenish Ridge and become loco lized in t~e synclinol vol ley between the two r idges. Geol. Soc. Americo Bu ll., v. 66, p . 663-684. Yakima Basal t Olivinre bc,olt c l,o wa, ~rupted contemporaneously from o low ,hield volcano on the Lincoln Ploteou north of © the mapped area. C Flow,, block but weather brown to brownish groy, -----, 1961, Keechelu, problem, Co,ccde Mounto ins, Washington; Northw.ast Sci,, v, 35, p. 39-57. ~ generally 70 to 150 feet thick; locol interloyen of 0 diotomite and tu llcceou, sond;tone; two- tier jointing; ~ upper port ve,iculcr grading upward to ocori oceou, top; -0 C intersertal and generolly nonporphyritic; contoln plo 0 gioclo,e (An J, clinopyroxene (+2V=44°-38°), opaque © 50 C mineral,, ond l;ttl<> or no olivine (Fo ); gloss c<>nlenl © 80 u 10 to 30 p,arcent, lc,col ly chorged with c linopyroxene - 0 1 - opaque minerol;, end opotjte; chlorophoeite or its :a A A' A" olterotion product, generolly fil l interstices. Bose of FEET
forma tion not exposed, totol thickn•" unknown ,000 POAVIIIE RLOG€ •OOO ' '- OAK HIU on ~ '," -~QTbs • ·~ aooo '• • 2 Qo 2000•-j--;;;:--- ' / I QTb I . Qb "V"/ ,000 ' Ty N --, _ _, ... '" -···art; GEOLOGIC SECTION A LONG LINE A-A'-A" :,, -'-- B' J' ~ Approximate mean declination, 1957 ' ' • B • B' FEET ! '0 ' • 6000 ' ' 0 2 3 4 5 6 Miles 5000 - OT" 4000 SCALE 0Tb ~000 ------/ ...... -...... 1-- __ --- - .. =:::::::- -- Te~ - ---- _..- ·-- _.- _..- - _.- _...,,,-' .,,,,- r-~-...... ~ r---- ...___ ------__:___------Te, QTb ~ r------\ -' •• :::--==- ==...... : --- ·.-:::: ------/ /- ---- tOOO = --= ------,,------~ - ======-~__:=.- - --_...,/ / :-:----; r-=:--:: ==- -==-== =- -- -==-.:::.:::::: == ==~ ------_:::- ____ ·-i---=:------·.-= ==------=------==------__ SOIi l EV£l--'--- "'"'-~"°'~------==-==-==-==-c.. _J ______=-==C::----===:_--~-----==--""''-..<~--"'--'-=--'c-=--/ ...... __...... -----...::------=-===----'"-==~------=:c-=------==-==-==-====-==-=='-'==-==-=-----L
T :t N. N GEOLOGIC SECTION ALONG LINE B-B'
F R R I E R 16 120°45' R I E Geology mapped 1958-59
Bose from Army Map Service Topographic For sale by Department of Conservation, O lympia, Wash. Quadrangles, Yakima and The Price $1.00 Dalles, 1,250,000 GEOLOGY OF THE SIMCOE MOUNTAINS VOLCANIC AREA, WASHINGTON By Richard A. Sheppard 1967