STATE OF WASHINGTON DEPARTMENT OF NATURAL RESOURCES BRIAN J. BOYLE, Commissioner of Public Lands ART STEARNS, Supervisor DIVISION OF GEOLOGY AND EARTH RESOURCES RAYMOND LASMANIS, State Geologist GEOLOGIC MAP GM-29 GEOLOGIC MAP OF THE YAKIMA QUADRANGLE, WASHINGTON By R. D. BENTLEY AND NEWELL P. CAMPBELL Prepared in cooperation with U.S. Department of Energy Contract oe.ACOS-81 ·RL 10297 1983 GEOLOG IC MAP DIVISION OF GEOLOGY AND EARTH RESOURCES PREPARED IN COOPERATION WITH THE U.S. DEPARTMENT OF ENERGY UNDER GM-29 WASHINGTON STATE DEPARTMENT OF NATURAL RESOURCES DESCRIPTION OF MAP UNITS RAYMOND LASMAN IS, State Geolog ist CONTRACT NUMBER DE-AC06-8 1-RL10297 BR !AN J. BOYLE, Commissioner of Public Lands ART STEARNS, Supervisor A' SURFICIAL DEPOSITS laboratory results indicate transitional after demagnetization (Aietman, 1966) ; resembles plagioclase-phyric flows of Frenchman Springs Member, but phenocrysts generally morn abundant, and smaller in average size; one flow in map area Oa, ALLUVIUM, sidestream facies - Stream deposits of illt, sand, and gravel dominantly of basaltic composition; CORRELATION OF MAP UNITS largely confined to valley bottoms; may include local lacustrine, paludal, and eolian deposits in depressions Tf Frenchman Springs Member Undifferentiated - Fresh exposures are gray to black; gray to reddish-brown on deposited by tributaries of the Yakima River (sidestream facies of Waitt, 1979] weathered surfaces; medium- to coarse"1 rained; high ly to very sparsely plagioclase phyric flows of French­ SEDIMENTARY ROCK UNITS man Springs chemical type (Wright and others, 19731; normal magnetic polarity (Rietman. 1966); thin a,m ALLUVIUM. mainstream facies - Stream deposits of silt, sand, and grave l of mixed lithologies; largely confined sedimentary interbeds common; one to three flows in map area; lower flows commonly pillowed at base to va lley bottoms; may include local lacustrine, paludal, and eolian deposits in depressior,s; deposited directly by the Yokima River (mainstream facies of Waitt. 1979) Tf, Flows of Union Gap, Frenchman Springs Member - Fresh exposures are gray-black; weathers gray to reddish.gray; fine- to medium.grained; generally aphyric with rare plagioclase phenocrysts up to 2 cm; j Ofs Oe Ols Oaf TERRACE DEPOSITS - Stream deposits of silt, sand. and gravel of diverse composition; largelv confir,ed to the >­ Yakima River d rainage system; poorly indurated and moderately to slightly weathered clasts; divided into phanocrysts average 1 to 5 glomerocrysts per 10 square metars surface area; colonnade w ith 1.5-2.0 m "'<( Ot2, middle level, and into Gt1, lower level diameter columns and locally pil lowed base; some flows have hackly entablature; Frenchman a,, Springs chemical type (Wright and others, 1973); normal magnetic polarity; one flow over most of '-? .._? z ' - map area, locally 3 or 4 flows on Ahtanum Ridge, This unit is probably equivalent to Mackin's (1961 l Oafo "'w Oaf ALLUVIAL FAN DEPOSITS - Sand and gravel of diverse composition with basalt clasts dominant in lorger sizes; cone shaped with little or no caliche development; surface relatively undissected Sand Hollow and Sentinel Gap flows, but exact correlation is uncertair, • \ ~ ' IGNEOUS ROCK UNITS =, Tfk Flow of Kelley Holl ow, Frenchman Springs Member - Fresh exposures are gray.black;weathers to reddish­ Qls LANDSUDE DEPOSITS - Clay, silt, sand, and gravel; unstratified and poorly sorted; surface often hummocky; • a deposited by rotational-translational slide1 and flows gray: tine- to medium"1rained; phyric with abundant plagioclase phenocrysts and glomerocrysts up to a" 0: 2 cm; phenocryst abundance highly variable from 1 to 100 glomerocrysts per square meter surface a, EOLIAN DEPOSITS - Silt and fine sand; pale orange to brown; locally contains multiple caliche and tephra area; thir, entab1ature and well-developed colonnade with 0.5-1.5 m diameter columns; Frenchman -... beds; includes the Palouse Formation and all younger loess Sprir,gs chemical type (Wright and others, 1973); normal magnetic polarity 1,, Gato OLDER ALLUVIAL FAN DEPOSITS - Sand and gravel; semiconsolidated fanglomerate; primarily basalt clasts Tfb Flow of Badger Gap, Frenchman Springs Member - Fresh exposures am gray-black; weathers gray to 1, '· ' cemented by iron-stained clays; surface of fans frequently dissected and capped by well-developed cal iche reddish.gray; fine- to medium.grained; generally aphyric with rare plagioclase phenocrysts up to 2 cm; . - f, phenocrysts average 1 to 5 glomerocrysts per 10 square meters surface area; colonnade with 1.5-2.0 m ..... ' ... ..,.. .... J QI, CATASTROPHIC FLOOD SLACKWATER SEOIMENTS - Silt, with minor amounts of sand ond gravel; rhyth· diameter columns and locally pillowed base; locally hackly entablature; Frenchman Springs chemical '',na!i'- : "I.~~.,,;, unconformity mically bedded and graded; deposited by lower energy slackwater floods or surges of catastrophic floods; type (Wright and others, 1973); normal magnetic polarity. This flow is the Sand Hollow flow of includes the Touchet beds; locally contains elastic dikes, tephra beds, end ice-rafted fragments JI <",., ' ..Jeu 1 Bentley ( 1977) i : / Q,o Tl ETON ANDES ITE - Hypersthene-augite, plagioclase, phyric andesite; single intraconyon flow confined to t he Tfg Ginkgo flows. Frenchman Springs Member - Fresh exposures are gray-black; weathers to reddish-gray; flne• lower Naches River droinage to medium"1rained; phyric with abundant plagioclase phenocrysts and glomerocrysu up to 2 cm; 100 to 200 glomerocrysts per square meter surface area; thin entablature and well-developed colonnade QTog OLDER GRAVEL REMNANTS - Coarse sand and gravel; alluvial fan and terrace remnants;dominantly basalt with 0.5-1.5 m diameter columns and pillowed b,;ise; Frenchman Springs chemical type (Wright and GJ clasts; slightly to moderauly weathered with local fine sand and slit lenses; associated with steep slopes of others, 1973); normal magnetic polarity; laboratory results indicate a south excursion incEnation with anticlinal ridges of the Yakima fold belt; age uncertain but may be in part correlative with Thorp Gravel normal polarity (Sheriff and Bentley, in press); one to two flows in the map area .._ Ttm Tts THORP GRAVEL - Coarse sand and grnvel; moderately to highly weathered and poorly indurated stream ter­ Saddle race deposits related to the Yakima River drainage; locally divided into mainstream facies of mixed li1holo­ Mountains GRANDE RONDE BASALT lt .. G gies (Ttm); and into basalt-dominant sidestream facies {Tts); base of unit commonly unconformable near Basalt ridges and cooformable in basins with underlying Ellensburg units Unnamed basa lt flows, nonporphyritic to very SParsely plagioclase.phyric, genera lly f;ne..grained and petro• Ts graphically nondistinct; chemical composition varies within a broad field named Grande Ronde chemical ELLENSBURG FORMATION type (formerly called Yskima chemical type by Wright and others, 1973); divided into two chemical types - high MgO and low MgO (Swanson and others, 1979); also divided into magnetostratigraphic units on the G basis of dominant magnetic polarity To" ELLENSBURG FORMATION UNDIFFERENTIATED ~ Gravel, sand, silt, and clay - white to light reddish­ brown; weakly to moderately indurated fluvia! and leharic deposits; dominated by pumiceous dacitic, Flows of normal magnetic polarity - N2 of Swanson and others ( 1979) - >­ andesitic, and basaltic cl~sts; grades dowrlward into thin units of fluvial sand and cl(ly. locally pebbly sand, Upper part of unit contains four or five flows of high MgO Grande Ronde chemical type I Swanson and "'<( with mixed vo lcanic clasts ond locall y hyaloclastic units; base defined as the top of the lowermost flow of others, 1979); this unit is the Sentinel Bluffs sequence of Myers and others (1979); fresh exposures are B the Columbia River Basalt Group, but the uoit includes all conformably underlying sediments of similar gray-black; weathers reddish-brown and gray; flows are commonly moderately microphyric with 1 to 3 mm f­ lithologv beyond the lowermost Columbia River basalt flow pinchout; top of unit defined as below Thorp long, equant plagioclase phenocrysts in a flne- to medium-grained basalt; many flows are multitiered flows; "'w Gravel or other Pliocene(?)Plaistocene units; to the east intertongues with flows of the Yakima Basalt four flows form this unit in the map area; the lowest flow is the McCoy chemical subtype I Long and others, , f- Subgroup 1980) T,o Lower part of the N2 contains flows of low MgO Grande Ronde chemical type_ Two to four flows ere G Ts Selah Member of Schmlncke (1967) - Clay, silt, sand, and gravel;white to light reddish brown;weak!y to fine'1rained, dense, black, aphyric basalt with thick, massive, black, hackly entablatures over colonnades. ~· ·oa~ ' l. moderately indureted fluvial and laharic deposits; dominated by dacitic. andesitic, and pumiceous sedimentary interbeds are common et the top and bottom of this unit. but invasive relations (Byerly and ,~ clasts; stratigraphic position defined by overlying Pomona Member of the Saddle Mouotains Basalt and Swanson, 1978) obscure their continuity and none are shown on the map, The upper flow in this unit is next basalt stratigraphically below the Umtanum flow (Umtanum chemical subtype of Myers and others, 1979) Tfo I Vantage Member - Clay, silt, and coarse sand; wh ite to tan; weakly to moderately indurated fluvial de­ Wanapum posits; dominated by dacitic and andesitlc grains and loca l pumiceous clasts; stratigraphic