t l WHC-SA-1764-FP

_OV09 199_ Late Cenozoic Structure and o s T/ Stratigraphy of South-Central Washington

S. P. Reidel N. P. Campbell K. R. Fecht K. A. Lindsey

To bepublishedin SecondSymposiumonthe GeologyofWasaington

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Late Cenozoic Structure and Stratigraphy of South-Central Washington

S, P. Reidel l_, N. P. Campbell3, K. R, Fechtz, and K. A, Lindsey z 1Ocoscicnces Group We.stingho_e HartfordCompany Richland, WA 99352 2AI,w at Department of Geology Washington State Univenit 7 Pullman, WA 99164 3 Yakima Valley College Yakima, WA 98907

ABSTRACT The structural framework of the Columbia Basin began developing before Columbia Rivet' Basalt Group (CRBG) volcanism. Prior to 17.5 Ms, the eastern partof the basin was a relatively stable area, with a basement of Paleozoic and older crystalline rock, The western part 'wu an areaof sub,siderite in which large volumes of sediment and volcanic rocks accumulated. The boundarybetween the two "" parts is a suture zone between the stable crotonand secreted tertanes. Concurrent with eruption of the CRBG, anticlinal ridges of the Yakima Fold Belt (_'B) were growing undernorth-south compression. Topographic expression of these features,however, was later masked by the large volume of CRBG basalt flowing west from fissures in the easternColumbia Basin. The folds continued to develop after cessation of volcanism (ca. 6 Ma), leading to asmuch u iI,,000m of structural relief in the past 10 million years. Rates of subsidence and fold growth in theColumbia Basin decreased from the Miocene to Recent. Shortening acro_s the entire YFB probably does not exceed 25 km. Post-CRBG evolution of the Columbia Basin is recorded principally in folding and faulting in the YFB and sediments deposited in thebasins. The accompanying te_tonism resulted in lateral migration of major depositional systems into subsiding structural lows. Although known late Cenozoic faults are on anticlinal ridge.s,earthquake focal mechanisms and contemporary strain measurements indicate most stress release is occurring in the synclinal areas under no_-th-southcompression. There is no obvious correlation between focal mechanisms for earth- quakes whose loci are in the CRBG and the location of known faults. High in situ stress values help to explain the occurrence of microseismicity in theColumbia Basin but not the paRem. Micmseismicity appears to occur in unaltered fresh basalt. Faulted basalt associ- ated with the Y'FB is highly brecciated and commonly altered to clay. The high stress, abundance of ground water in conf'mcd aquifers of the CRBG, and altered basalt in fault zones suggest that the frontal faults on the anticlinal ridges probably have some aseismic deformation.

INTRODUCTION isa northeast-trendianngticlinoriumthatextends250 km The Columbia Basinisan intermontanebasinbetweenthe from theOregon CascadestotheeasternpartoftheColum- Cascade Range and theRocky Mountains thatisfilledby biaBasin.The easternmostpartof thebasinconstitutesthe Cenozoicvolcanicrocksand sediments.Thisbasinforms fourthsubprovinceand willnotbe discussedinthispaper. the northernpartof both the Columbia Plateauphysic- In thecentraland westernpartsof theColumL_a Basin, graphicprovince (Fenneman, 1931) and the Columbia theColumbia RiverBasaltGroup (CRBG) overliesTerti- River flood-basalt pro¢irlce (Reidel and Hooper, 1989). ary continental sedimentary rocks and is overlain by Within the Columbia Basin are four structural subdivi- younger Tertiary and Quaternary fluvial and glaciofluvial sions or subprovinces (Fig. 1). The Yakima Fold Belt deposits (Campbell, 1989; Reidel and others, 1989b; Smith (YFB) is a series of anticlinal ridges and synclinal valleys and others, 1989; U.S. Department of Energy, 1988). In the in the western and central parts of the basin. Structural eastern part, a thin (< 100 m) sedimentary unit separates the trends range from northwest to northeast bu_ are predomi- basalt and underlying crystalline basement and a thin nantly east-west. The Palouse Slope forms the eastern sub- (<50 m) veneer of eolian sediments overlies the basalt province of the basin; it shows little deformation, with only (Reidel and others, 1989b). a few faults and low-amplitude, long.wavelength folds on In this paper, we discuss the Late Cenozoic structure an otherwise gently westward-dipping paleoslope (Swan- and stratigraphy of the Columbia Basin. We focus largely son and others, 1980). A third subprovince, the Blue Moun- on the period following eruption of the last voluminous wains, forms the southern border of the Columbia Basin. It flood-basalt flows of the Saddle Mountains Basalt, those of the Elephant Mountain Member (10.5 Ms). However, we

BULJ..b'TIN80 Reide/ 9/1193 1 WHC-SA-1764-FP 2 REGIONAL GEOLOGY OF WASHINGTON STATE

¢ 49" , _ tonic "blocks" or uplifts

WASHINGTON sIt, MarlesI _ rthatocksexposeand havepre-Tertiarya north- Embayrnent._. west-trending structural 48" grain. Along the northeast and east margins of the // Palouse Columbia Basin, the Subprovlnce 47' CRBG laps onto Paleo- •.. • '--. zoic rocks and Precam.

. e' ! brian metasedimentary ... rocks interspersed with •" crystalline rocks. These _-,-_ ':-,, ." 'Clearwater rialIJ Ia_;iL ... _.. __ . | ,,,': Subprovlncef . .._.. ,...,:'_:.mbayrnent( 48' ' tinasedcludiem:eProntaryterozorocksicmoe.f

\ _l_i ...... "..(.M'_B__untalns "_ andthe WBindermelt Supergroup,ere Group ' :...... s prince _, miogeosynclinal lower ': 6:_ :, as' Paleozoic shallow ma- line rocks, rocks associ. Iser ated with the Kootenay :: arc, granitic rocks of the 44" Idaho Batholith, and 0L I I100Kilometers ExtentoftheColumbia; otherJurassicandCreta- 1 , _ - i River Basalt Group ceous intrusions (Stoffel 0 lOOMIles "OREGON : IDAHO and others, 1991). The

.... _ l I .... I . L I 4 _ . structural grain of these 12s" 123" 12a" a_g' 1_7. _ls" rocks is north to north- Figure I. The Columbia Basin. Shown arc the areal extent of the Columbia River Basalt Group, the east. four major structural-tectonic subprovinces, the Pasco Basin, and the Olympic--Wallowa lineament. To the south and southwest, lower to mid- dle Tertiary (Paleogene) trace the development of the Columbia Basin from before volcanic rocks and related volcaniclastic rocks directly un- the CRBG eruptions to the present because tectonic events derlie the CRBG. The rocks include tufts, lahars, and tuf- that occurred during this time are closely related, faceous sedimentary rocks interbedded with rhyolite, an- desite, and basalt flows and breccias; these are primarily STRATIGRAPHY assigned to the Clarno and John Day Formations. Older The generalized stratigraphy of the Columbia Basin is (Permian--Cretaceous) volcaniclastic sedimentary rocks shown in Figure 2 and summarized in Table 1. Most of the and metasedimentary rocks of accreted intra-arc and vol. rocks exposed in the basin are the CRBG, intercalated sedi- canic.arc origin are exposed along the southeast margin of mentary rocks of the Ellensburg Formation, and younger the CRBG (Walker and MacLeod, 1991). sedimentary rocks that include the gingold Formation, To the west, younger volcanic rocks erupted from the Snipes Mountain conglomerate, Thorp Gravel (not shown High Cascades cover the CRBG and obscure the older on Fig. 2), the Hanford formation, and other localized rocks. Rare inliers of older Paleozoic rocks, such as the strata. In this report, the Hanford formation includes all de- Rimrock inlier, are exposed as erosional windows in posits of cataclysmic Pleistocene floods, including those younger vole.hie rocks. from glacial Lake Missoula and the Columbia River sys- Sedimentary rocks related to those along the northwest tern. margin are thought to be present under the interior of the the Stratigraphy Older than the Columbia Basin. However, units exposed along north, east, and south margins of the CRBG probably contributed Columbia River Basalt Group to the sedimentarypackagebecausethey wereextensively Rocksolder than the CRBG are exposedalong themargin erodedby west-flowingrivers (Fechtandothers,1987)and of the Columbia Basin, Their stratigraphy is complexand their depositsaccumulatedin the subsidingwesternpartof varies widely in both age and lithology (Campbell, 1989). the basin. Along the northwest margin, a series of sedimentary basins formed in early Tertiary time (Tabor and others, 1984; Campbell, 1989). These basins are now separated by tec-

911193 Reidel BULLETIN 80 2 WHC-SA-1764-FP 4 " REGIONAL GEOLOGY OF WASHINGTON STATE i i Table 1. Strati_'aphic units and characteristics. Palouse Formation, Latah Formation, and other loess deposits not includ_l

Unit Age Thlekneu Distribution Llthology Stratlgraphlc trends Tectonic Implications

Columbia River 17.5 Me- as much as Extent defines the Tholeiitic flood.basalt Older, more voluminous Records stability in the Basalt Group 6 Ma 4 km in Columbia Plateau flows units cover entire area; eastern Columbia central younger,thinner units Basin, subsidencein Columbia occurincestem and central thecentral andwestern Basin ColumbiaBasin basin, and Miocene uplift of anticlinal ridges

Upper Bllensbur8 10 Me- as much as Nile, Selah, Basalt sidestrnam Volcaniclastic sediment_ Shifting channel Formation (Fecht 4.72 Me 350 m in Yaktma, _ttitaa, gravels, lahars, and most common in west; deposits reflect and others, 1987; t"O.28 Yakima and Satus and volcaniclastic sediments stllciclastlc sediments in dlsplacm'nentof river Smith+ 1988) Basin Toppenish basins; derived from Cascade east; gravels record courses caused by ridge also inGolden- Range,siliciclastics channelsystempositions uplift andbasin dale area deposited by subsidence, especially Columbia River YakimaRiverand ColumbiaRiversouth- westof Pasco Basin

Snipes Mountain <8.5 Ms-. 30-150 m Lower Yakima Quartzose gravel and Linear channel tracts from Records Columbia Conllomerate 8.5 Ma valley and across siliciclastic sands; Sunnyside Gap up Moxee River course prior to (Schminke, 1964; western Horse interbedded volcani- and Yakima valleys and diversion into Pasco Fecht and e_hers, Heaven Hills; also elastic sediments then across Horse Heaven Basin 1987; Smith, 1988) east Toppenish common in eastern Hills to Goidendale srna basin Toppenish Basin Ringold Formation <8.5 Ms-- as much as Peace Basin, north Fluvial gravels and Gravelly alluvial tracts Records initial post _ecJ1t and others, >3.4 Ma 185 m side of Saddle sands, overbank deposits, mixed with basin-wide CRBG Columbia River 19871 Lindsey, Mountains, and lacustrine deposits, and overbank systems deposits in Pasco 1991a, b) Walls Walla basin alluvial fan deposits dominate lower partof Basin, shifting channel section; sharply overlain courses reflect by a sandy alluvial system syndepositionai uplift that, in turn, grades on basin margins; up-section into cyclic large lakes reflect lacustrine deposits regionalchangesin river gradients

Lake deposits <4.7 morn than Lower Yakima Laminated silts Equivalent to Large lakes form as overlying Snipes :L-0.3Ma 30 m valley near and fine.grained upper Ellensbur8 a result of regional Mountain Sunnyside and sandstone Formation; laterally gradientchanges Conllomernte Grangerandon correlativewith upper (Smith, 1988) AhtanumRidge Ringoldlake deposits(?)

Thorp Gravel <3.64 as muchas Kittttas and Selah Basaltic sidestream Old terraces of the Record uplift and (Wail/,, 1979; :L-O.74Ma 200 m basins, and south gravels and poly- Yakima River erosion of Cascades Bendey end to 3.7 into Yakima basin mictic mainstream and Yakimafolds. Campbell,1983; :C0.M2a asfarasToppenishgravelsdepositedasan Campbell, 1983; alluvial wedge off the Fochtand others, Cascades 1987; Smith, 1988) Plidcun4_and <3.5- as much as Regional Pedogenic carbonates, Unconformably overlies Deposited after post. Pleistocene strata -1 Ma 10m distribution in basaltic alluvium, eolian middle Pliocene and older 3.5 ]Viabus.level (U.S. l:)ept, of basins and on deposits, muitilithologic (>3.5 Me) strata; change that led to Energy, 1988; uplifts quartzose gravels discontinuous horizons in regional incision of Baker and others, and around basins and main rivers; records 199!) uplifted on ridges more recent uplift of anticlinal ridges Hartford formation <1 Me- as much as Peace Basin, Pebble to bouldei gravel, Common throughout Strata locally offset ('Focht and others, - 12 ka 70 m Toppenish, sand, and laminated silts region, mostly below by faults recording !987; Baker and Yakima, and Wails deposited by cataclysmic elevations of approx. Pleistocene deformation others1991), Wallsbasins,and floodwamrsreleased imateiy 1200ft flood deposits from glacialLake throughout the Missoula Columbia Basin

Quaternary <:2Ma 0 to 7J m Regional Locally derived alluvial Laterally discontinuous Folded and faulted alluvium (Baker and andcolluviaideposits stratacommonon basin depositsrecordnee- others, 1991) margins and on uplifted tectonic deformation ridges in region

911193 R,idel BULLETIN 80 3 ' WHC'SA-1764-FP STRATIGRAPHY AND STRUCTURE, SOUTH.CENTRAL WASHINGTON 3

A _ocFormath ion Occursin the westernbasin; in the central andeasternba- Gks [ sin, epiclastic deposits of the ancestral Clearwater and Co- Eolian and alluvium lumbia Rivers form the dominant lithoiogies (Fecht and Toucl_etBeds others, 1982, 1987).

500ka <,i '__ ,-_.___':=_-_ uisssandsoumfloogdravel5 Post-Columbia RiverBasaltStratigraphy ...-:._,_ / ano Most post-CRBO sediments are confined to the synclinal 700 ka _ 'i'__"._ ' ,]"_cene,aaPre.Missoula,rly'PalousPliocane'inl.eerPleisval lo- valleys of the YFB The sedimentary record is incomplete, a.4M= __ , but it is a direct reflection of the structural development of :_t _r_ the Columbia Basin (Fecht and others, 1987). The upper :_"_ Miocene to middle P!iocene record of the Columbia River "_ _ _ Lacustrine• filldeposits _[_ system in the Columbia Basin is representedby the upper '_: _ Ellensburg Formation, Ringold Formation, and Snipes ] Mountain conglomerate, The Thorp Gravel (-3.7 Ma) river .2 i"_3 kaixefluviad slandano terrace deposits record the post-CRBG history of the upper i_7 ove_anksequence Yakima River (Waitt, 1979; Campbell, 1983). Except for ,,. _.,. local deposits (for example, the "Pliocene-Pleistocene P_[_ unit" and the "early Palousesoil" [U.S. Department of En- _ o oi";."1 ergy,1988]), there is a hiatus in the stratigraphic record ..._-- _,,_(_a_c_ GravelunitE between the end of the Ringold (3,4 Ma) andThorp Gravel (-3.7 Ma) deposition and the Pleistocene (1.6 Ma) depos- _ iravelunit C

.... Graveunil tB CRBG include: flood gravels and slackwater sediments of __. its.the HanfoPleistordceneforma.'ion;to Holocterraceene segradimevelsntsof ovethe rlColyingumbthia,e _F'.....-_¢'_ >" Gravel unit D Snake, and Yakima Rivers;and, in eastern Washington, eo- o_o_ GravelunitA lian deposits including the Palouse Formation (Keroher SnipesMountainConglomerate and others, 1966). 8,S Ma I_ - =_ ] SaddleMountain,' GEOLOGIC STRUCTURES J Basalt

14.SMa _ =0'_ / WanapumBasalt Flood-basalt t OF THE COLUMBIA BASIN

i GrandeRonde seaimenis The major structural features that underliethe Columbia = Basalt Basin are exposed along its west and north margins 17.015.6MaMa i_ __ t ,nierl:)sUmtanum Ridge, Yakima the area (Reidel and others, 1989b). Ridge, and Rattlesnake Ridge (the ridge immediately south Intercalated with, and in some places overlying, the of Yakima Ridge) (Fig. 3). CRBG are epiclastic and volcaniclastic sedimentary rocks The portion of the OWL that crosses the Columbia Ba. of the Ellensburg Formation (Waters, 1961; Swanson and sin is called the Cle Elum-Wallula deformed zone (CLEW; others, 1979a; Smith, 1988). Most voicaniclastic material

BULLETIN 80 R_idel 9/1193 t, Flgure3.Majorgeologifceatureisnm: ColumbiaBuin.Shown ar_thisHol Ranch-.Nan¢umRid8¢anticlinth¢e,Olymplc-Wal- Iowalineament(OWL), andmajorsurfac©structurAlsoes. shownartthiss infnrredlocationsofmajorsubbualtstructuraf¢latur_s andth=proposededgeofthecontin_tatlriton.

Kienleandothers,1977).Itisa 10.kin.wide,moderately RAW); and (3)theWallulafaultzone,extendingfrom diffuszeoneof anticlinesthathavea N50°W orientationWallulaGap southeastottheBlueMountains. ('Fig.3).As definedby G.A. Davis(inWashingtonPublic Northwestofd_eCRBG margin,numerousnorthwest. PowerSupplySystem,1981a),theCLEW consistsofthree andnorth-trendifngaultands shearzonesoftheStraight structurpartsal (I): a broadzoneofdeflectedoranomalous CreakfaultsystemliesubparalletoltheOWL (Taborand foldand faulttrendsextendingsouthfromthenorthwest others,1984).The Snoqualmiebatholithintrudetheses partofManastashRidge(intheCascadefoothilneals rthe faultbuts _snotcutby them,indicatingthatanymovement edgeoftheCRBG) toRattlesnakeMountain(2)', a narrow alongtheOWL atthewesternmarginoftheColumbiaBa- beltoftopographicalalliygneddomesanddoublyplunging sinmustbeo!derthanthebatholith,17to19.7Ma (Frizzell anticlinesextendingfromRattlesnakeMountaintoWallula andothers1984), . Gap,wheretheOWL crossestheColumbiaRiver(azone Thestructurasignifl icanceoftheOWL hasbeencalled commonly calledtheRattlesnake-Wallualaignmentor intoquestionby tworecentgeophysicalstudiesNeither. a

BULLETIN80 R¢id¢l 9/1193 5 WHC-SA-1764-FP 6 REGIONAL GEOLOGY OF WASHINGTON STATE

Table2. Characteristoficsanticlinarildges_;--mean;a = 1 standardevd iationR ;= range;NK = notknown;best approximation* s.tructurrealliefonyoungestbasalt

Length/ Rellef* Number of Segment Amount of Anticline width (maximum) Trend segments length Vergence shortening Geometry

Beeziey Hills- 160 km/ 430 m 230 o 4 _=40 0=20 S NK; <2 km Asymmetrical, mono¢linal Beeziey Coulee 5 km R=30 m 70

Badger Hills- 50 km/ 300 m 220 o 1 --- N NK; <2 km Asymmetrical, monoolinal Moses Stool 5-15 km

Frenchman Hills 100 km/ 200 m 90°-100 . 7 _..=14 o-.10 N NK; <2 km Asymmetrical, gentle to open 5-10 km 1_7 to 35

Saddle I10 km/ 550 m 90°-115 e 6 _.=14 eel0 N >3 km Asymmetrical, gentle to open, i Mountains 5-I0 km Re5 to 20 box fold

Manastash 55 km/ 370 m 120 o 4 _,=12 0=2.5 N NK; >3 km Asymmetrical, gentle to open, Ridge-Thrall 5-I0 km 17,=10to 15 8truedmre

Umtanum Ridge 110 km/ 520 m 90°-1300 9 _.=11 0=4.2 N 1-3 km Asymmetrical, tight to open, 3-10 km R=5 to 17 en echelon segments east end

Clemtn 35 knd 950 m 130 o 2 _.=l& 0=8 S NK; >1 km Asymmetrical Mountain "" 8 km R.=I3 to 23 "-

Yakima Ridge 100 km/ 550 m 135°-225 ° 12 Tt=12 0=8 N NK; :,3 km Asymmetrical, gentle to open, 5-I0 krn R=5 to30 en echelonsegmenu, box fold segments

Rattlesnake 85 km/ 800 m 310 e 11 L=9 0=6 N NK; >3 km Asymmetrical, tight to open, Mountain and 5-20 km R=5 to 25 faulted out hinge, doubly "rattles" plunging

Rattlesnake- 100 km/ 610 m 238°-1080 11 _,=9 0,4 N NK; >1 km Asymmetrical, gentle to open Ahtanum Ridge 5-8 km R=5 to 18

Toppenish Ridge 85 km/ 500 m 118°-258 ° 5 _.=17 0=7 N NK; >1 km Asymmetrical, tight to open 4-8 km I_I0 to28

Snipes Mountain 13 km/ 150 m 110 ° 3 13 km S NK;

Horse Heaven 185 ken/ 335- 115°-255 ° 21 _,=17 0=5 N >2 km; Asymmetrical, tight to open, Hills 5-30 km E; 1i00 m R=5 to 20 (0.67- en _helon subsidiary crest 2-7 km W 1.25 km) folds, box folds

Columbia Hills 170 km/ 250- 255 o 10 _15 0=6 S NK; >2 km Asymmetri_l, tight to open 5-I0 km 365 m I_6 to 23 doubly plunging, on echelon subsidiary crust folds,box folds

seismic profiling survey by Jarchow (1991) nor a gravity The HR-NR anticline was active in middle to late Mio- survey by Saltus (1991) could find any obvious geophysi- cone time, as demonstrated by thinning of basalt flows cal signature of the OWL below the CRBG. across it CReidel and others, 1989b). However, the e_st. Hog Ranch-Naneum Ridge Anticline trendingYakima folds show no apparentoffset by the cross structure(Campbell, 1989; Tabor and others, 1982; Kienle The Hog Ranch-Naneum Ridge (HR-NR) anticline is a andothers, 1977; Reidel and others, 1989b), nor is the I-IR- broad south-trending anticline in the CRBG that crosses NR anticline offset where the OWL--CLEW crosses it. the YFB at a nearly right angle. The anticline begins at the Growth of the HR-NRranticline continued from the Mio- north basalt margin on Naneum Ridge (at the south end of cone to the present time and is now delineated by the high- trtheendsStuartsoutbloheastck forandabsoouthwut 1e2stkmof andthe thciteynoturnsf Wenatsoucthheeto),- est structural points along the ridges that cross it. ward Presser, WA, where it separates the Toppenish basin White River.Naches River Fault Zone to the west from the Pasco Basin. This south-plunging The White River-Naches River Fault Zone (WR-NRFZ) structure passes through five Yakima folds and the OWL. (Fig. 3), a major fault zone that extends 90 km from Naches A gravity gradient and a series of gravity highs delineate to Enumclaw, WA, separates two domains of dissimilar part of the anticline in the subsurface. The southern exten, structure, stratigraphy, and topography (Campbell, 1988, siGn of the anticline appears to be a Bouguer gravity high 1989). To the northeast, structures strike N60oW; to the near the Washington-Oregon border southeast el'Presser, southwest, structures in pro-Tertiaryrocks trend N5°E to

9/I/93 Reidei BULLETIN 80 6 ',, WHC-SA-1764-FP , _\ STRATIGRAPHYAND STRUCTURE,SOUTH-CENTRAL WASHINGTON 7

' . /7 ...... / Table 3. Characteristics of major faults; NK = not known (best approximation) " Horizontal Vertical Sense of movement; Fault zone Length Trend offset off'set fault.plane dip Age of last movement

CLEW 290km 310" 0.-4Ion 0-800m mainlyreverse Quaternary;seeTable4 RAW(includes 125km 310" 0-4 km 0-800m mainlyreverse/some Quaternary;seeTable4 WallulaFaultZone) possiblestrip-slip Hitafaulstystem 135km 3300-3350 NK NK; verticaenleche, lon, Holocene(1936Milton. 0-900m andstrike.slip Frnwataearthqur ake); seeTable4 FrenchmanHills 100+km 270*-280' >300m -200m reverse,thrust;>45°5 >5120,000yr SaddleMountains 100km 2700-285* >2.5km 600m reverse;>60°5 <3.4Me,Quaternary- Holocene? Menastalh- 70 km 300* <1km -300m reverse,thrust >1 to3.4Ma HansenCreek Umtanum I10 km 270"-310' >300 m 1500m reverse,thrust;30..-70"S <13,000yr ClemenMountain 207km 310° NK -900m reverse,thrust;N Unknown YakimaRidge 120+km 225"-..45' NK -500m reverse,thrust;S, <1 Ma ,_.. locallyN .- Rattlesnake- 100km 58'-315_ NK -800m reverse,thrust;S >13,000yr AhumumRidge ToppenishRidge 65-90km 2580-298* NK -500m reverse,thrust;S Holocene:seeCamp bellandBentley(1981) HorseHeavenHills 200+km 2450-295o NK -335- reverse,thrust;S Unknown ll00m ColumbiHaills 160km 2450 NK; !km -365m reverse,thrus7t0;°N Unknown Northwest-trendin8 40-120ion 320* <100m <100m strike.slip,vertical Holocene faults (dipreversal)

N2OoW.TheWR-NRFZ probableyxtenduns derthebasalt Northwest.TrendingWrenchFaults atleastasfarasKonnowocPass(Fig3). andeithepretal. A seriesofnorthwest-trenddexingtra,strike-l slipwrench lelsorcrosscutstheHR-NR anticliThene.WR-NRFZ is faultsispresentintheCRBG westof120'longitudande themajorstructuretrendinigntotheColumbiaBasinthat theFIR-NRanticli(Nneewcomb,1969,1970;Shannon& canbedemonstrattoedbeafundamentalstructuralbound. Wilson,Inc.19, 73;Bentleandy others1980, Swanson; and an/inrockbelowtheCRBG. others,197%,1981And; erson,1987)These. areconjugate LeavenworthFaultZone anden-echelfaulton ands geneticalrelylatean-d echelon TheLeavenworthfaulistpartofa faultzonethatconsistsfoldsthathavea mean strikofe N40ow.Many canbe ofaserieofsnorthwest-trendinhigh-angleg faultsandas. tracedformorethan100km butdonotextendbeyondthe CRBG. Thesewrenchfaultcross sandoffsesteveral sociatedtightfoldsthatmarksthesouthwestsideofthe Chiwaukumgraben('Fig.3).Atthebasaltmargin,thefault Yakimafolds,buttheydo notappeartohavemorethan I00m totadlisplaceme(Andnt erson,1987). passessoutheastundertheCRBG inalignmentwiththe HR-NR anticliThene. Leavenworthfaultisassumedto TheYakimaFolds continueunderthebasaltalongtheHR-NR anticliandne The YFB subprovincecoversabout14,000kmz ofthe tohavebeenafactoirnitsdevelopme(Camnt pbel1989)l, . westerCnolumbiaBasin(FigI). andformedasbasalt Saltu(199D,s howevers,uggestsitdoesnot.continuun.e flowsandintercalatedsedimentwserefoldeandd faulted derneaththebasalt, undernorth-south-dircomectedpression.Thereadeirsre- OtherStructureMsarginaltotheColumbiaBasin ferredto_Tabl2eands 3andtherecentcompilationofstruc- Othermajorstructurincludes itheng Entiatfault,Methow, turalfeaturfoesrtheColumbiaBasinbyTolanandReidel Republiandc, Kellegrrabens,andnumeroufaus lassoci-t:, (1989)w,hichupdatepslatII.20e ofMyers,Priceandoth. ers(I979). atedwiththeKootenayArcappeartodieoutortheimar g- nitudeissignificantlyreducedbeforereachintheg basalt Mostofthepresentstructurareliel inftheColumbiBae- marginTh. ereforwee,donotconsiderthemsignificanttec- sinhasdevelopesdincaboute i0.5Ma whenthelastrues- tonicelementisntheColumbiBasina sivaoutpourinofglava,theElephantMountainMemberof ' theSaddlMounte ainBass alt(Fig.2),buriedmuchofthe

BULLETIN 80 Re_del 911193 7 8 REGIONAL GEOLOGY OF WASHINGTON STATE

YAKIMA WHC-SA-1764-FPFOLD BELT PALOUSE SLOPE

12 i° 120 ° PASCO BASIN 1t 9° 1180 _ , • t .... , I I YM 1.33 HOG RANCH.NANEUM RIDG| ANTICLINE OetlO in see,ion ic! HAR|OR OIKI SWARM DARe;ILL NO. 1 _ L,,, ,,,, .L_ , ,,,,, J , ,., _. f .-- _.. , ,, :- i ,, j , , f,, ----

i _ .'.' ':.;; .... '.';.':., : .",.::.'..'.'.";, ",'." .'.',,

A IDGI OF CONT1NINTAL CRATON A'

4(I O Sg SADDLE MOUN"TA!NS RAT'P,,,ISNAKE MOUNT, AiN 460 08' 1210 1 20 0 1 '_90 118 t'l UM"rANUM YAKIMA RSH 1 HORSE HiAVIN HILLS - '- ...... _ ' ..... ' . 470 I

_LoMrrE_s 460

• Hydrocarbon exploration borehole [_ Columbia River Basalt Group _ Terttary sedtmenls _ Basement rock

Figure4. No,r_-sou_andgenerallycut-westcrossectionsthrough_h(c:entralColumbiabum (modifi:dfromRcideal ndo_mm, 1989b).

central C-_lumbiaBasin. The main deformationis concen- Swansonand others,1979b;Hagood, 1986; Rcidei, 1984, trated in the YFB; thereis only minordeformationon the 1988;Anderson,198'/) that areemergentat groundsurface. Pa]ouseSlope. The topsof lava flows atgroundsurfacebecometheplanes TheYFB consistsof anticlinal ridgesseparatedby syn- of low.angle thrust faulting, Where erosion provides c]inalvalleys. The folds arctypically segmented,andmost deeperexposures,thesefrontal faultsareshownto besteep have north vergence. However, someanticlines, such as reversefaults: the fault in theColumbia watergap in the Columbia HilLs,Cieman Mountain, anda few segmentsof FrenchmanHills dips 45 degreessouth(Grolier andBing- other ridges, have a south vergence.Fold length ranges ham, 1971), and the fault in the Columbia Hills at Rock from 1 to more than 100 ks; fold wavelengthsrangefrom Creek, W'A, dips 50-./0 degreesnorth (Swansonand o1.11. severalkilometers toas muchas 20 km (Table2). Thefolds ers, 1_79b). are segmented by crosscutting faults and folds (Reidel, Hydrocarbon exploration boreholes provide direct evi- 1984; Reidel and others, 1989b). Structural relief is typi- dence for the dips of these frontal faults. Reidel and others cally less than 600 m but varies along the length of the fold. (1989b) have shown that the Saddle Mountains fault must The greatest structural relief along the Frenchman Hills, dip more than 60 degrees where the ShelI.ARCO BN 1.9 the Saddle Mountains, Umtanum Ridge, and Yakima Ridge borehole was drilled (Fig. 3). Drilling through the Umtan- occurs where they intersect the north-trending HR-NR an- um fault near Priest Rapids Dam suggests that this fault ticline (Fig. 3). dips at least 30 degrees (Puget Sound Power and Light, Anticlines of the Yakima Fold Belt have various trends, 1982) but perhaps as steeply as 60 degrees southward under ranging from N50*W through east.west to N50*E. Abrupt the ridge (Price, 1982; Price and Watkinson, 1989). changes in trend occur along individual anticlines at seg- Total shortening across the YFB is less than 25 km sent boundaries, giving these anticlines a disjointed ap- (Reidel and others, 1989b), or about 5 perc_:nt of the fold pearance along their length. This is most apparent where belt width. Crustal shortening is difficult to estimate, how. anticlines cross the zone of the CLEW. On a regional scale, ever. Typically, shortening caused by folding is 1 to parts of the fold belt typically have dominant directional 1.5 ks, but the amount of shortening caused by faulting is trends. The anticlines lying within the CLEW zone typi- generally unknown. Estimates for shortening due to fault- cally trend NS0*W (Fig. 3). However, anticlines southwest ing alone range from several hundreds of meters to as much of the CLEW have a dominant NS0*E trend (Swanson and as 4 km (Table 3). others, 1979b; Reidel and others, 1989b; Tolan and Reidel, Typical synclines are structurally low areas formed be- 1989) (Fig. 3), and the trend of anticlines northeast of the tween the gently dipping limb of one anticline and the CLEW, such as the Saddle Mountains and Frenchman steeply dipping limb of another. The steep limb was thrust Hills, is dominantly east-west. Anticlines that extend up on the gently dipping limb of the neighboring anticline across the entire fold belt, such as Umtanum and Yakima to form the syncline. Few synclines were formed by simple Ridges, have varied trends that reflect the dominant trends synclinal folding of the basalt. of the areas they cross. Although the faults are rarely exposed, nearly all the THE PRE.MIDDLE MIOCENE steep forelimbs of the asymmetrical anticlines are faulted. COLUMBIA BASIN These frontal fault zones _ typically consist of imbri- The Columbia Basin as we now see it reflects structural cated thrusts (Bentley, 1977; Golf, 1981; R. D. Bentley in elements that formed prior to flood-basalt volcanism. This

911193 Re_del BULLETIN 80 8 WHC-SA-II64-FP STRATIGRAPHY AND STRUC7"URE, SOUTtf-CENTRAL WASHINGTON 9

section of our paper provides an interpretation of the struc- 1984, 1987). This location is also marked by the prominent tural setting of the Columbia Basin prior to the eruption of aeromagnetic anomaly shown by Swanson and others the CRBG. Our interpretation is based on data from the last (1979c) for the Ice Harbor dike swarm and that extends as two decades of geophysical surveys and from deep hydro- far south as the east side of Wallula Gap. This boundary carbon exploration boreholes in the Columbia Basin, both between craton and basin may cross the CLEW and inter- combined with our field observations, sect the structurally similar Hite fault boundary near The YFB and Palouse Slope overlie the two major pre. Pendleton, OR. CRBG structural features of the Columbia Basin (Reidel The HR-NR anticline parallels the eastern margin of and others, 1989b). The YFB lies on a large pre-basait ba- the pre.CRBG basin and appears to divide it into two parts. sin filled with as much as 7,000 m of continental sedi- Campbell and Banning (1985)have interpreted pre-CRBO ments. The Palouse Slope subprovince overlies a crystal, rocks under the HR-NR anticline as part of a horst, but re- line basement high; only a thin (<100 m) discontinuous suits from a recent seismic profile (Jarehow, 1991)suggest sediment package separates the basalt and basement, that the HR-NR anticline may not involve basement. We The crystalline basement underlying the Palouse Slope suggest that the Pasco Basin is underlain by a northwest- (Fig. 4) has been penetrated by two boreholes (the Darcell trending graben between the HR-NR anticline and the su- and Basalt Explorer, Fig. 3). This basement is essentially ture zone. The we.stern graben fault may only involve the metasedimentary rock composed of quartz, feldspar, and basalt _nd sediment and not the basement rock. Tertiary mica. It resembles the Addy Quartzite and certain Precam. sedimentary and volcaniclastic rocks west of the I-IR-NR brian Belt Supergroup rocks. We interpret this basement to anticline extend beyond the margin of the CRBG and form be part o_'the old continental craton that has remained part of the Cascade Range. The western basin margin is not fairly stable except along its west and south margins, Mohl faulted, as implied by the rift model of Catchings and and Theissen (1989) extended the southern boundary by Mooney (1988); the pre-CRBG sedimentary rocks continue extrapolating gravity data from l.ewiston, ID, as far west as across the present Cascade Range and were arched upward Pomeroy, WA (Mohl, 1985). The rock penetrated by the with the Cascade Range to form the present western bound- Darcell boreho!e (Fig. 3) indicates that the craton must also ary of the Columbia Basin. This model is supported by gee- extend west and south from Pomeroy. We suggest that the physical studies (Rohay and Malone, 1983; Rohay and oth. trace of the southern cratonic margin is reflected at the sur. ers, 1985; (}lover, 1985; Zervas and Crosson, 1986) face by the Hire fault zone (Fig. 3), the major fault system suggesting that the Columbia Basin is not a failed rift basin that forms the western margin of the Blue Mountains be- but perhaps simply a back-arc basin. tween Pomeroy and Pendleton, OR, and has been the locus The Blue Mountains uplift forms the s_uthern boundary of many historic earthquakes (U.S. Department of Energy, of the pre-CRBG basin, although the bou,tlary is not pre- 1988). cisely located. The boundary may lie near the present Blue The YFB is underlain by a thick sequence of sediments Mountains crest because a thick sequence of sedimentary that was first recognized in deep hydrocarbon exploration rock lies north of the crest below the basalt near the Wash. boreholes (Campbell and Banning, 1985). On the basis of ington.--Oregon border (Fox and Reidel, 1987). We inter- seismic refraction survey data, Catchings and Mooney pret this boundary to coincide with Beeson and others' (1988) interpret this as a failed rift basin. Other studies us. (1989) east-trending Columbia Transarc lowland (Fig, 3) ing additional geophysical data sets (Rohay and Malone, that forms the low area extending along the Washington- 1983; Rohay and others, 1985; Glover, 1985; Zervas and Oregon border through the Columbia Gorge. The Columbia Crosson, 1986), however, question this interpretation. Transarc lowland and the pre-CRBG basin combine to pro- These studiesdo not "see" any deepcrust or mantle evi- ducean apparentnortheast-trendingtroughthrough theCo- dence for a failed rift basin, lumbia Basin, The thickest pre-CRBG sediment package The pre-CRBG basin above the crystalline basement is lies along this trend; in addition, more CRBG flows are filled with deposits consisting primarily of Paleocene and found along the trough than elsewhere in the basin. The Eocene continental sediments and some Oligocene volcani, lowland was the main pathway for CRBG lavas flowing be- elastic sediments (Campbell and Banning, 1985; Campbell, tween the vent area and western Oregon and Washington 1989), Reidel and others (1989b) interpreted the suture (Reidel and Tolan, 1992). zone between the pre-CRBG basin and craton to coincide with the Ice Harbor dike swarm (Fig. 4). They also inter- TItE MIDDLE MIOCENE COLUMBIA BASIN preted the location of the dike swarm to have been control- Borehole, geophysical, and stratigraphic data (Bergstrom led by this fundamental crustal boundary, Reidel and others and others, 1987; Catchings and Mooney, 1988; Reidel and (1992) suggested that this boundary is the suture zone be- others, 1989b) indicate that the CRBG thins onto the Pa- tween the continental craton and accreted terranes. Further- louse Slope and thickens into the YFB (Fig. 4). The CRBG more, they suggested that the suture is oriented approxi- ranges from 500 to 1,500 m thick on the Palouse Slope, but mutely N10oW and is marked at the surface by the ice it abruptly thickens to as much as 4,000 m in the Pasco Harbor dikes and the boundary between the Saddle Gap and Basin area (Reidel and others, 1982, 1989b). Regional Eagle Lakes segments of the Saddle Mountains (Reidel, thickness patterns for both the CRBG and underlying Ter-

BULLETIN 80 Reidtl 911193 9 WHC-SA-1764-FP 10 REGIONAL GEOLOGY OF WASHINGTON STATE

"- Gap _

SaddleMountains SaddleMountainl

...... Columbia River-....-" .-'-_.,-.,..-'_-_.'-_-..--_-'_-.."_"_'_".,.-."...: . £ _.',,...... -_- - floodplatn.overbank a system-_-- Mtn,'- ..... _ y,lkio_,l CableM_. "-...... -"." =_eke floodplain.overbank""------system...... InAke m ,.,,- i Cap.... SunnysideGap " ice Harbor Member :eHarborMember.,,d -" aoncity flow front ..... -- - flow front _.¢1_4

- "- ...... - '-HorseHeaven HeAven)tillsII1_'_ __.'_"-. .,;'_@I SaImon.Clearwater Sa,toon.Clea_ater _d..T_.._ "" river system riversystem._T_ c,, w.,,=,.,.it'm_l, A B

FIsure5. Generalizedevolutionof theCohunbiaRiver ,, systeinm thecentralColumbiaBuindu$[ntllhelatMeio-

"_. c(A)eneSanipesndPlioMoceuntane(Modiitimn feepifrepdroomFxeimatch_tdI0.0colythtoer8,s,190Me87),. Sentinel Gap (B) Approximately8.0 to 6.0 Ha. (C)After6.0 Ha. Z SaddleMountelm approximately 1 cm/yr initially and decreased to 3 x 10"3 River cm/yr in the late Miocene (Reidelandothers,1989b), ..fl..oo_clplain-overbank During the eruptionof the CRBG, the anticlinal ridges system:.:-" were topographic highs against which the basalt flows _" _,,_.;._, --..--"-"-_"" Rethinnideledanwdithotheelersvati, 19o8n9bd;urAinndgermsopnla, c1987)emen. Flt(Roweidtheicknel, 1984;ss .... "snake ....._...... "-".______variations provide a means to estimate fold growth rates ,m ,.,..,m .... {Reidel19, 84).The ridgegrs ewatabout0.25mm/yr dur- Sunny,,deCa_ ing initial eruption of the CRBG (17-15,6 Me); the rate de. :" creasedtoabout0.04 mmlyr duringthewaningphases -__-':_-6_ty (15,6.-10Me)(Reide.5 l,1984;Reidelandothers19, 89b), -- By theend of themassiveeruptionsoftheCRBG (10,5Me),most of theColumbiaBasinwas a shallow, HorseHllvenHill, bowl-shaped,nearly featureless plain. The massive erup- Saline teens had buried most of the structural and topographic re- riversystem lief. In the western pan of the Columbia Basin, standing w,,,uclapa above theplainwereonlytheanticlinraidgesl notinun- C datedbyyounger flows, Acrossthis plainflowed theances- tral ColumbiaRiver audits main tributaries,includingthe Liar),sedimentary rocks indicate that the pre-CRBG basin Salmon--Clearwater,Yakima, and Palous¢Rivers. was subsidingrelate,, :o the Blue MountainsandPalouse Slope from at least the Paleocene or Eocene though the THE LATE MIOCENE TO MIDDLE PLIOCENE Miocene. By far the most significant regional tectonic ac. COLUMBIA BASIN tivity was continued subsidence in the basin. The subaerial Post.CRBG tectonic history of the Columbia Basin is re. nature of the CRBG indicates that subsidence continued as corded in the Yakima folds and post-CRBO sediments. Al. long as basalt was being erupted and that basalt accumula- luvial.lacustrine sediments (Table 1) deposited primarily teen kept pace with subsidence (Reidel and others, 1982, by the Columbia River system show that the Yakima folds 1989a, 1989b)_ Subsidence rates from 17 to 15.6 Ma were were still growing and displacing river channels (Fecht and others, 1987). The structural evolution, as reflected in these

9/1193 R¢ldel BULLETIN 80 10 WHC-SA-1764-FP STRATIGRAPHY AND STRUCTURE, SOUTH-CENTRAL WASHINGTON 11

FrenchmanHills L Sentinel Cap Sentinel Gap ' Z e z • ColumbiaRiver-".... inferredSandy _ .... brai..... dp_la3in- - - channRiverel ..... -"- -_ )lain.overbank "-- -

system ---'_-._ --. GablMt.e .:'-overbank _ ._-:_ _ _,,,,,, ---_s_y2t..- em ------I " Rattlesnake. :._--..-_'_ Rattlesnake hills /d ..... "_ Hills/ / ;almon- Sunnlnt_ Gap "Salmon. SunnysideGap earwater Clearwater alluvial fan

HorseHe=yen Hills HorseHeaven

Wallula Gap -e.- Wallula Cap A B Figure6. Gcner-alizedinterpretationofthepalcogeogra- phyof the Puco Basin duringeachof the three phasesof the RingoldFormationdeposition.The first phase(A) =:o FrenchmanHills endedapproximately 6.0 Ma; the secondphase(B) ap- _' proximately5.0 Ma;andthe thirdphase(C)approximately _ _ SentinelGap 3.4ML _

sediments, is interpreted from: (1) the lateral distribution of facies, (2) changes in depositional style, and (3) struc- tural deformation. Lateral Distribution of Facies Changes in the facies distribution in post-CRBG sediments =_ are one of the best records of the post-CRBG history of the _am=nake Columbia Basin. Sand and gravel in fluvial channels mark Hm, ,//,, the locations of major drainages. Lesser alluvial fans and Sunnyside Gap sidestream alluvial sequences were deposited adjacent to ? the main rivers. Ridge uplift and basin subsidence caused lateral shifts in these depositional environments over time (Fecht and others 1987; Smith, 1988; Lindsey, 1991). During the waning phase of CRBG eruptions (12.5- H,,=, 8.5 Ma), the Columbia River flowed south across the YFB. The post-CRBG pre-Ringold channel (upper Ellensburg WallulaGap Formation and Snipes Mountain Conglomerate) of the Co- C lumbia River passed across the western Pasco Basin, enter- ing at Sentinel Gap (Reidel, 1984, 1987) and exiting near Sunnyside Gap (Fig. 5_A). From there the river flowed Concurrent with the eastward shift in the Columbia southwest toward Goldendale. At about 8 Ma, the Colum- River, alluvial wedges deposited in the Yakima River bia River began to shift eastward into the central Pasco Ba- drainage system prograded eastward (Smith, 1988). These sin, occupying a water gap over the eastern end of Rattle- wedges are seen in the upper Ellensburg FormaOon and snake Mountain near Benton City (Fecht and others, 1987; Thorp Gravel. Fig. 5B). By middle Ringold time (approximately 6 Ma), Changes in Depositional Style tthhee PCasolumbiaco BasinRiveatrWhadallushila fGtedap i(Fig.ts pos5Citio),naagains it do, esexinowting Three major changes in depositional style are found in the (Fecht and others, 1987). Ringold Formation. Each is marked by rapid, apparendy basin-wide transitions. The first change occurred at ap-

BULLETIN 80 Reidel 911193 11 WHC-SA-1764-FP 12 REGIONAL GEOLOGY OF WASIIlNGTON STATE

(or combinations of factors) influenced the Columbia River. Distribution of Deformed Post-CRBG Sediments Uplifted and faulted Ringold and coeval sediments flank most ridges in the central Columbia Basin Fi_.7; Reidel, 1984, 1987; Reidel and others, 1989b). The ele. vations at which they are found reflect the amount of structural development on the ridges after the sediments were deposited. Deformed Pliocene and Pleistocene sedi. ments also are found on many ridges. QUATERNARY AND YOUNGER DEFORMATION IN THE COLUMBIA BASIN Probably all geologic structures of the Co. lumbia Basin had.developed their present relief by the end of the Pleistocene. Evi. Figure 7. In this view tothe west,the RingoldFormationoverliesthe Elephant dence for continued growth of the YFB is aMountrea.Thiains oMemberutcroppofingtheliesSaoddlen theMountainnorth sidesBaofsthealt,RCRBG,attlesninaketheMSnivelyountainsBatruscin- mainly in the frontal fault zones. Although ture and is part of the frontal fault zone. The ElephantMountainMemberhas not common, evidence of Pleistocene beenthnastnorthonto the RingoldFormation. faulting has been found at many locations across the YFB ('Fig. 8; Tab!e 4). Young faults have been described at Toppenish proximately 6 Ma and is seen as a shift from gravelly braid- Ridge, at Union Gap in Ahtanum Ridge, on Gable Moun- plain and basin-wide paleosol systems of the lower part of tain along Umtanum Ridge, in the Columbia Hills anti- the Ringold Formation _ to the sandy alluvial sys- cline, and along the CLEW (Table 4). Age relations are terns of the middle part (Fig. 6B). The second shift in de- generally poorly constrained, however, but they suggest positional style, which had occurred by 5.0 Ma, is marked that faulting has continued since the last cataclysmic flood by the replacement of sandy alluvial systems by wide. (approximately 13,000 yr B.P.). The minimum age of this spread lacustrine conditions (Fig. 6C). Lacustrine deposits faulting is not known, but no seismically active faults have are found throughout the region, including the Yakima Val- yet been identified. Younger glaciofluvial sediments of the ley (Smith, 1988) and north of the Saddle Mountains Hanford formation locally record some of the youngest de. (Reidel, 1984, 1987). Lacustrine conditions and Ringold formation in the Columbia Basin. deposition ended with region-wide incision of the Colum- bia River systembeginning approximately 3.4 Ma. Incision Toppenish Ridge resulted in the removal of more than 100 m of Ringold sec- Campbell and Bentley (1980, 1981) describe a 0.5- to 2.2- tion in the central part of the Pasco Basin. Many of the Plio. km-wide zone of nearly 100 surface ruptures along a 32- cene and Pleistocene pedogenic carbonates in sediments km-long segment of the north flank of Toppenish Ridge overlying the Ringold Formation and found on the anticli. Fi(_. 9 . The scarps are subparallel to the ridge trend and nal ridges began to form following initiation of this inci- range from 0.1 km to 3 km in length. The lowest scarp (Mill sion. Creek) is a thrust fault (Fil_, 10), but all other are high. These changes in depositional style are inferred to be angle normal faults. Individual ruptures have displace- related to regional factors that led to abruptchanges in gra. ments as great as 4 m; organic material in the ruptures • dient in the Columbia River system. The limited evidence yields 14Cages of 505 :t:160 yr and 620 :t: 135 yr (Campbell available suggests gradients could have been influenced and Bentley, 1981). by: (1) changes in uplift rates where the Columbia River Ahtanum Ridge crossed the southern extension of the HR-NR anticline; (2) increased Cascadian volcanism in the Columbia River A Quaternary or younger fault was exposed during high- Gorge between 6 and 3 Ma (Tolan and Beeson, 1984; Tolan way construction near Union Gap on Ahtanum Ridge and others, 1984); (3) upstream changes in detrital input F(._s. 8 and 1..H.).A high-angle reverse fault offsets Yakima into the Columbia River system; and (,1) headward erosion River terrace gravels by at least 7 m, juxtaposing them as base level dropped in the lower Columbia River. It is not against the basalt of Ginkgo, Frenchman Springs Member yet possible to determine precisely which of these factors (N. P. Campbell, tn Washington Public Power Supply Sys- tem, 198I). A questionable U-Th caliche age of 30,000 yr

9/1/93 Reld¢l BULLETIN80 12

,r Figure8,LocationofQuaternary--HolocenefaultsandpossibleQuaternary-HolocenefaultsintheCohtmbiBaa sinS.eeTables4 and5 fordescriptioofthens faults, wasobtainedfortheterracegravel(Campbes ll,1983)The, Umtanum Ridge-GableMountain faultgougeappearstobecappedby undeformed13,000- GIaciofluvialdeposits13,000yearsoldareoffsetasmuch yr-oldslackwaterfloodsedimentsbut, exposuresI km to as6,5cm bythecentralGableMountainfaul(Put getSound theeastrevealfaulteds!ackwatersediments(N.P.Camp- PowerandLight,1982)attheeastendofUmtanum Ridge bell,unpub,data,1992), (Fig.8),Thistearfaulthasacomponentofreversmoe ve- ment;itshows increasinoffsetg inprogressiveolylder units,

8 ULLETIN _0 /te idol 911193 13 WHC-SA-1764-FP 14 REGIONAL GEOLOGY OF WASHINGTON STATE

,,

Table 4, Quaternary-Holocene faults in the Columbia Basin; NK -' not known; see Fig. 8 for locations

Primer7 structural Ale of'let Senseof' Amount of Fault feature movement movement movement Location Source of Information ...... -- ,,,:,l, . : : ...... _...... :..... _-- _ ..... + : ...... I. CentralFerry PalouseSlope Pleistocene? sinistral 1 to i.5 m centersec.22, TI2N, R4OE FoundationServices, oblique.slip Inc. (1980, p,25) 2. Them Hollow Hire Fault early strike.slip nut SWt/,tNEt/4sec,2, T4N, ShannonA Wilson,Inc. System Holocene? dt ermined R35E (1979, p, 28) 3. Buroker Wellula Fault Pleistocene thrust fault with >i m see,31, TTN, R3TE ShannonA Wilson,Inc. System to early compoqent of (19"79, p. 16-1"7); Holocefle? iJnistraJ strike.slip ' Foundation ServJcal, Inc. (1980, p, 41.44) 4. Little Dry Creek WallulaFault Pleistocene? normal 0.5 m NEt/,tsec. 11,T4N, R3b'E Shannon& Wilson,Inc. System (1979, p.33-34) 5. Barrett WallulaFault late dextral varied, SWV_qEI/4See. 25,T6N, Shannonk Wilton,inc. System Pleistocene oblique.slip 2 to $0 crn R34E (1979, p, 33) to Holocene?

6. Milton. WallulaFault Holo_ne dextral Iround bruka8 • SEt/4I_, 18,TSN, R.35E Shannon& Wilson,Inc. Freewater System (i936) strike.slip not located (1979, p. 36) 7, Promon_ry WellulsFauh Pleistocene? normal NK sec. 10,T6N, R37E "- Shannon& Wilson,inc. Point System (1979, p,40); FoundationServices, Inc.(1980,p.40.41) 8. Wallule (near WeJlulaFault Pleistocene? strike.slipor NK sec. 12,T6N, P,32E Farooqui(19'19,p, 8-9) Warm Springs System oblique.slip Canyon) 9, Umapine Wsllule Fault Pleistocene?- oblique-slip NK sec,15,TSN, P,,34E Mann (1991) System Holocene and Lewis 10. Wallula (near Weilula Fault early not determined NK see.3, T6N, R32E Oles8 (1977, p, 2.R Van|ycle System Holocene KS.Kg);Farooqui Canyon) (1979, p.9.10) 11, FinleyQuarry Cle Elum- Pleistocene? reverse NK sec.3, T'TN, R30E FarooquiandThorns Wsllula (1980, p, 4-8) lineament- Domain IZ

12. Central Gable Gable Mountain late reverie -6 cm sec. 19, TI3N, R27E Pule Sound Power and Mountain Anticline Pleistocene? LJlht Company (1981, ('Yaklma fold) p. 34.45) 13. Mill Cr_k thrust Toppenish Holocene both normal as muchas Area between CampbellandBendey fault and Ridle end reverse 4 m let. 46'15'-460|9'N, (1981, p, 519.$24) numerous (Yakim8 fold) Ions, 120"22'.-i22°40'W unnamedfaults

14, Union Gap Ahtanum Ridge Pleistocene? reverse approximately TI2N, RIgE Wsshinlton Public ('Yakimefold) 7 m PowerSupplySystem (1981,p. 7..JK.53); Oeomevix Consultants, Inc. (1988, p. 47.$4) i i! i

Columbia Hills OR (Table4). The widespreaddistribution of Quaternary On thewestern side of the Columbia Basin, Andersonand faultingin theColumbia Basin,however,suggeststhatthe Tolan (1986) report a Holocene fault cutting Pleistocene CLEW does not have any more or fewer Quaternary faults slackwater flood sediments on the south side of the Colum- than other partsof the YFB. bin Hills anticline near Goldendale. Other Localities CLEW Undocumented and (or) unpublished da_ for otherQuater. Quaternary deformation has been reported at 15 localities nary or younger faults include the following _, along the CLEW (Washington Public Power Supply Sys- Fig. 8): Manastash Ridge (Geomatrix Consultants, Inc., tern, 1981; U.S. Department of Energy, 1988; Tolan and 1988), Boylston Mountains (R. D. Bentley, Central Wash. Reidel, 1989) between Kennewick and Milton Freewater, Univ., oral commun., 1983), Cleman Mountain (Geomatrix

9/I/93 R, id,I BUL,L,_TIN 80 1/, WHC-SA-1764-FP . STRATIGRAPHY AND STRUCTURE, SOUTH.CENTRAL WAStlINGTON 15

Consultants, Inc., 1988; N. P. Campbell, unpub, data), Yakima Ridge (R. D, Ben. dey, oral commun., 1990), Medicine Val- ley (Geomatrix Consultants, Inc., 1988), Hog Ranch-Naneum Ridge anticline (R. D. Bentley, oral commun., 1986), Tamarack Springs (Campbell, 1983), Frenchman Hills and Smyrna Bench, Saddle Mountains (Geomatrix Consultants, Inc,, 1990; West and Shaffer, 1989; Shaffer and West, 1989; S. P, Reidel, unpub, data), Wenas Valley (West, 1987), Kittitas Valley (Geomatrix Consultants, Inc,, 1989), and Ahtanum Ridge (N. P. Campbell, unpub, data; Gee- matrix Consultants, inc,, 1989). There appears to be no pattern of fault. ing in the YFB that would suggest that Qua- ternary-Holocene faulting is more concen- t trated in one part of the basin than in i another. Rather, the distribution seems to fJ suggest that the entire fold belt has contin. Figure9. Holocenefaulton ToppenishRidgenearYakima,WA.View south- ued to develop in a pattern similar to that of cut alongthe northflank of ToppsnishRidgeat the faultscarp.Thefaultscarp the Pliocene and Miocene, offsets theCRBG, alluvium,and lees.. Note thedivertedgully. CONTEMPORARY STRESS .' AND STRAIN . Regional Stress Indicators .,, In situ stress for the Columbia Basin has been deter- mined from geodetic surveys and earthquake focal mechanism solutions. Geodetic surveys (Prescott and Savage, 1984) across the Pasco Basin suggest north- south shortening at a rate of.0.27 at:0.22 microstrain/yr. The principal strain directions are N3*W ± 34* at 0.06 ± 0.013 microstrain/yr and N87*E ± 34* at .0.024 ± 0.014 microstrain/yr). This rate is not statistically sig- nificant at the 95 percent confidence level, however, and the measurements are within the error limits of the recording instruments. Focal mechanism solutions are more definitive, and they indicate that the maximum principal stress is gen- erally north-south and the minimum principal stress is near vertical (U.S, Department of Energy, 1988). Seis. micity occurs in three stratigraphic zones: the CRBG, the sub-basalt sedimentary rocks, and the crystalline basement. Most of the seismicity is concentrated in the CRBG and the crystalline basement. No seismic events have been associated with known faults; seismicity tends to be concentrated in the synclinal areas _; U.S, Department of Energy, 1988).

Figure10. Trenchthrough theMill Creekthrustfault at base of the north limb of Toppenish Ridge,.This fault placespumiciteof theupperEllensburgFormationoverf_! gravels and a wedge of soil on the left side of the photo- graph.

BULLETIN80 Reidel 9/I/93 15 WHC-SA-1764-FP 16 REGIONAl.,GEOLOGY OF WASHINGTON STATE

TableS. LocalitiesofsuspectedQuaternary-HolocenefaultsintheColumbia Basin;NK = notknown; seeFig.8 forlocations ...... : _ _ ,,,...... PrimarystructuralAge oflet Senseof Amount of Fault feature movement movement movement Location Source of information

15,Unnamed Serviceanticline Late strike.slip NK SEI/_WI/4sac.28,T6N, FoundationServices, Pleistocene? R28E Inc.(1980,p.48-49) 16. Luna Butte Columbia Hills Early dextral NK sac. 8, T3N,RI8E Anderson and Tolan (Yakima Fold) Holocene strike.slip (1986, p. 82) 17. Kittiuls Valley(3 Kittitas Basin Pleistocene? non'nil 2 m? Area between Waits(1979) faults) (YakimaFold) {at. 47°00'-.47'10"N, Ions,120'7J'-120°45'W 18. SmyrnaBench Saddle Late normal.reverse 6 m? TiS-16N, R25-27E OeomatrixConsultants, Mountains Pleistocene- inc. (1990); Westand (Yakima Fold) Holocene7 $haffer (1989) 19. FrenchmanHills Frenchman Holocene reverse 2 m? TI'I-I8N, R27-29E OeomatrixConsultanu, (2 sejments) Hills Inc. (1990); Shafferend (Yakima Fold) West(1988) 20. WestCanal FrenchmanHills Pleistocene reverse 1-3 m T18N R23E Orolier andBiniham (Yakima Fold) (1971); Geomatrix ,.. . ConsultantsInc, .(1990) 21. Pinto PintoRidje Pleistocene NK NK let. 47'30 ,'N, G6omatrixConsultants, long,119'15"W inc,(1990) . -- ...... ___ __.

The onlyassociationbetweenscismicityand faultsis Geodeticmeasurementsand,inparticular,thepattern on thecastflankof theSmyrna anticlineon theSad_ile ofsvismtcitindy icatethatthemaximum stressintheCo. Mountains(Reidel,unpub,data)Th. isisa segmentbound, lumbiaBasinishorizontanorl,th-southcompression arybetweentheSmyrna Benchand SaddleGap segments I.L_Th.)e.intermediatsteressishorizontaland east.west, ofReidcl(1984,1987).ScismicityoccursnorthoftheSad- andtheminimum stresissverticalTh.esedataareconsis- dieMountainson thewestsideofa suspecteddeepfault tentwithgeologicevidence(Reideandl others19, 89b)sug- markingthebounGaryandon thesouthsideoftheSaddle gestingthattheColumbiaBasinhasbeen undernorth- Mountainson theeastsideoftheboundary.A timeanalysis southcompressionsinceatleasttheMioceneand thatthe ofthemicroseismicishowsty thatthisdeepsuspectedfault samestresspatterncor4tinutesoday. controlths epatternofearthquakoccurre ence. ContemporaryStressintheCold

"It,' . Creek Syncline Core disking and spal]ing in coreholes drilled in theColdCreeksynclin¢,central Columbia Basin, indicate high in $itu stress (U.S.Department of Energy, 1988). Core disking _ occurs when drill corefracturesinto thin disks during drilling. Borehole spalling or breakout is also an indicator of high de. viatoric stress and suggests thatthe in situ stress is not distributed lithostatically. . Spelling occurs inthe direction of least ,, horizontal compression. The consistent east-west (FilzT!_)orientation ofbore- holespelling alsoindicatesthatthe maxi- mum horizontalcompressionis oriented generallynorth-south. StressMagnitude at Depth Hydraulicfracturingiscurrentlythemost widely usedmethodtodirectlydetermine FigureII.Roadcualot ngInterstateHighway90atUnionGapinwhichaHolo- themagnitudofe insitustressHy.draulic canefault is exposedF, renchmaSnpringsMember,SaddleMount_nsBasalt, fracturingtests wereconductedin bore- CRBG,isOvustsouthoverterracegravelof theYdcimaRiver,V='ticalre.b_ is holes at about 1 km depth in the upper fora retainingwall alongthehighway.

9/1/93 Reidet BUL_#V 80 16 WHC-SA-1764-FP STRATIGRAPHY AND STRUCTURE, SOUTH.CENTRAL WASHINGTON 17 t

119e 45' 118045" t@ O O

0 " _ EXPLANATION Magnitude ¢ e • 1.0. .9 e O ,,_ O 2.o.2.9

cO0 ,'o",,,," _o ' O(D._4.3.0.o3..4.99

® 0 ,' (9 0 FrenchmanHills Ol O0 0 ' 0 0 ® 0 Hanford ., ® SaddleMountains t C_3 Site 0 @ Gable Mountain I

@ eC) (9 (_ YaklmaRidge

(Raw) ¢ ¢ HorsoHeavenHilis 0 O

% 0 SCALE

_ ,, I ...... i" 1 ® e o o 0 ,0m , 0 46"

Flgure 12. Locationsof allrnicroseismiecventsrecordedfrom March 1969to,lanua_1989 inthecentralColumbil Buin, pan of the Grande Ronde Basalt in the Cold Creek syncline meet is possible on an east.striking reverse fault that dips (U.$. Department of Energy, 1988). The results indicated 60 to 65 degrees and has an effective friction angle of 33 that the maximum horizontal stress ranges from 52.6 to degrees or less along the fault plane. A comparison of shear 67.4 MPa (7,630-9,780 lbf/in 2) and the minimum horizon- strengths (Byerlee, 1978) to test results on the properties of tel stress ranges from 30.3 to 35,7 MPa (4,400-5,180 CRBG joint surfaces (U.S. Department of Energy, 1988) lbf/in2). The ratio of average horizontal stress [(oH + suggests that slip could occur on a fault plane in the present o'h)12] to the vertical stress (o'v) ranges from 1.41 to 2.14, stress field. with a mean value of 1,77 ± 0.20. This ratio is close to the The regional pattern of Quaternary and Holocene fault- higher ..nd of known stress conditions at comparable ing indicates that the hypothesis of Kim and ot,4ers (1986) depths at other locations (Fig. !6). The mean orientation of is correct, but the pattern of microseismicity is inconsistent induced fractures, and thus the direction of the maximum with the fault distribution. Microseismicity occurs in syn- horizontal stress, is consistent with north-south compres, clinal areas where the CRBG is typically fresh, unaltered, sion (Paillet and Kim, 1987). and competent. Microseismicity is apparently absent from In Situ Stress, Faults, and Microseismicity frontal faults on anticlinal ridges. This suggests that the ridges are deforming aseismically or that they are not mov. Given the high in situ stress conditions in the central Co- ing and have locked up. lumbia Basin, Kim and others (1986) suggested that move.

BULLETIN 80 Reidtl 9111P3 17 WHC-SA-1764-FP 18 REGIONAL GEOLOGY OF WASHINGTON STATE

1250 1200 11'50 5o0 soo

CANADA _'_"PO

1 . It ' !

\, %

, WASHINGTON [ , '

I I O

o , 450 ° ,.;,_ O.==ON ,

EXPLANATION Earthquakefocal mechanisms- parallelto --.7_q-- Topollraphiccontour,inmeters ¢omprussionadirectionl _. -- Exlm_sionaflutures - primarilynormalfaulu or Borehole breakouts- parallelto a combinationof normalandstrike.slipfaults comi_ssionaldirection ..,--- Sldke-slip faults Hydraulic fracturinl stressmeasuremenu- parallelto cornpressionaidirection _..-- Comprussionalfeatures- primarily thrust faults or reverse fault= Volcanic ventalillnrnent- parallelto five or =noracontemporaneouQuaternaryl volcanoes .... Seismicity- focal ofientetion;=nalnitude unknown

Figure 13, Sl_'¢ssorientation in the Pacific Northwest (modified from Zobzck amdothers, 1992).

It isdifficulttoimaginewhythestrongc, ompetentrock situscessisrelievedbymicroseismicit(yseismiccreep)in in thesynclineswouldcontinuallyexhibitwidespreadmi. thecompetentbasaltof thesynclineaa,ndthat thereis a croseismicacdvitywhile the incompetenwet, ak,altered componenotf_eismic movemenint thefaultzoneswhere basaltsin the presenceof abundantgroundwaterin the theincompetenbat saltgougeis lubricatebyd groundwater. CRBGaquiferswouldnotmoveandappm'entlbey locked up.Theregionahigl hinsitestresmus stbeactinong the SUMMARY AND CONCLUSIONS anticlinarildgesS.ome insightintothisproblemcomes TheColumbiBasa inistheproducoft deformatithatonbe. fromexaminingthefrontalfaultzoneson theanticlinalganearliyntheTertiarypri,otortheeruptiofontheCRBG, ridges.Thefaultsaremarkedbyhighlybrecciatbasaed lt;andcontinuestoday,TheColumbiBaasinhastwofunds. faulgot ugeiscommonlyalteredtoclay.We suggesthatt in mentapartl ismportanttothepost.CRBGgeologihcistory g11193 Reide.l BULLETIN 80 18 . WHC-SA-II64-FP STRATIGRAPHYAND STRUCTURE, SOUTH.CENTRALWAStt/NGTON 19

_!] IORIHOtl IPItLINa

HORIZONTAl. _

&ITPtINlIIMUUM t

"! MAXIMUM HORIZONTAL STlqtlll

Figure1$.Generalizepadtternofborehospdle linginMe ColdCreek=ynclLneRe. drawnfromU,S.Departmenoft Energ(t988).y

sincethelateMioceneas, well asthe deposiUonaIpattern of the post.basaltsediments. Therateof deformationin theColumbiaBasinhasde- clinedsincethemid-Miocene,thatis, therateofbasinsub- sidenceandridgegrowthhavebothdeclined.Thepresent rateof ridgegrowthis estimatedat 0,04 mmlyr,andsubsi. " : denceinthebasinisestimatedtobe3x10"_mm/yr, ' Microseismicity, high in situ stress conditions, and areasof QuaternaryandHolocenefaultingindicatethatthe basin is still experiencingnorth.southcompression.AI- . thoughknownlateCenozoicfaultsarefoundonanticlinal ridges,earthquakelocal mechanismsandstrainmeasure. menusuggestthatmostpresent-daystressreleaseisoccur- ringinthesynclinaarl eas.Noearthquakeeventshavebeen shown to be related to knownfaults.The high in situ stress intheColdCreeksyncltneexplainsthemicroseismiciinty that area, but the absenceof mtcroseismicityassociated .. with the anticlinalridges mayresultfroma componentof aseismic slip on weakened fault zones lubricatedwith groundwater. ACK,NOWLEDGMENTS Supportfor this study wasprovided by US r _,,,utmenoft Energy,OfficeofBasicEnergySciencesgrant.._nberDE. Figure14.DiskingincorefromborehoDe-6le ,Hanford FG06-9IERI4172toS,P.Reidealt WashingtonStatUeni, ' site, versitSuy,pportofthisstudydoesnotnecessaricolnsti,y tuteanendorsemenbyt theU,S.DepartmentofEnergyof of theColumbiaBasin,thePalouseSlopeandtheYFB.The theviewsexpressedinthisarticle. Palouse Slope is a stable, undeformedarea overlyingthe oldcontinentalcraton. The YFB overlies a large prebasalt REFERENCES CITED basinthathas beensubsidingsince the earlyTertiary.The Anderson,JamesLee,1987, Thestructuragel ology andagesof basin is divided by the HR-N'Ranticline. The edge of the deformationof a portion of the southwestColumbiaPlateau, cl,d continenertalatonisa suturezonethalit eastthejune- WuhingtonandOregon:UniversoiftSouy theCarnlifornia t:onofthetwostructuralsubprovincesandispresently DoctoofrPhilosophythesi2s,83p. markedby theIceHarbordikeswarmoftheCRBG. AndersoJamen, Les eTo; lanT,,L..1986,Agesofwrencfhaulting ThepatternofdeformatioinntheColumbiaBasinhas inhaterridgbase insouthws, eCstolumbiPalateaWuu,hington beendominatedbynorth-soucomthpression,andtheYFB andOregon[abstraGectl:ologicaSoclietofyAmericaAb- is the principalproductof this stress. Thisdeformationhas stractswithProgramsv., 18,no.2, p.82. also controlled the location of the Columbia River system

BULLETIN 80 Reialel 9/i/93 19 WHC-SA-1764-FP ...... 20 REGIONAL GEOLOGY OF WASHINGTON STATE i

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Doctorof Philosophy uhesis, 199 p,, 6 pl, inlltonPublicPower Supply SysternDockeno,t _0-460, PriceE.,H,; Waddnson,A,J,,1989,Structural geometryands_ain Preliminasaryfetyanalysirepors tAmendmen, t23,v.28,Ap- distributmwinthineuternUmtanum toldridge,south-ce,ntra[ l:_ndix 2R, Subappendix 2R K, 19 p, WMhington. In Reidel, S. P,; Hooper, P. R., editors, Volcanism OrolierM., l,;Binghun,J,W,,1971,Geologicmap ands_tions and tectonisLmntheColumbiaRiverflood.basaprovinclt e: ofpartsofGrant,Adams,andFranklinCounties,WMhington: GeologicaSlocietyofAmericaSpecialPaper239,p.265.281. U,S.OeololicaJ SurveyMiscellaneousGeologicInvestigationsPugetSoundPowerandLightCompany,198I,Skegit/Hanfonrud- Map [-589, 6 sh_, scale 1:62.500. clear project, preliminJu'y safety analysis report: Puget Sound Ha|God,M. C.,1986,Structureandevolutmnof_heHone Heaven PowerandLightCompany,7 v. Hillsinsouth-cenu'Waluhington:RockwellHanfordOpera. 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BULLETIN 80 R¢_d_l _t1/_/J 21 WHC-SA-IlB4-FP 22 REGIONALGEOLOGYOF WASHINGTONSTATE

Reidel,S. P.; Long, P. E.; Myen, C. W.; Mue, J.,1982,New evi- Swanson,D. A.; Wright, T. L.;Camp,V. E.:Gardner,J.N.; Helz, dencefor greaterthan3.2 km of ColumbiaRiverbasaltbeneath R.T.; Price,S.M.; Reidel,S. P.;Rms, M. E., i980, Reconnals. the c..,_tralColumbiaPlateau[abstract]:Eos (AmericanGeo- stncegeologicmapof theColumbiaRiverBMalt Group,Pull- physical Union Transactions), v, 63, no, 8, p, 173. man and Walla Walla quadrangles, southeast Wuhinston and Reidel, S. P.; Tolan, T, L., 1992, Eruption and emplacementof adjacentIdaho'.U.S. GeologicalSurveyMisceilaneo_ Geo. flood blulalt-.--An example from the large.volume Teepee Butte logic Investigatioru,Map I-I 139, 2 sheets, scale 1:250,000, member,ColumbiaRiver Basalt Group:GeologicalSocietyof Swanson,D. A.; Wright, T, L.; Hooper,P. R.; Bentley, R, D., America Bulletin, v, I04, no, 12, p, 1650.1671. !979a, Revisions in stratisraphic nomenclature of the Colum. Reidel,S. P.;Tolan, T. L.; Hooper,P. R.;Beeson,M. 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