Periglacial eolian deposits. Buff to light-brown, massive, homogenous, unconsolidated loessial silt; some water-laid material locally. Probably early Pleistocene.
Dark-gray to black, dense aphanitic basalt flows; commonly columnar jointed, less commonly irregularly and platy jointed; some flows vesicular, grading to scoriaceous; includes minor pillow lava, palagonite beds, and interbedded soil profiles and sedimentary beds; contains diatomite beds locally. Maximum thickness in south-central Washington may be in excess of 10,000 feet; much thinner in western Washington, where flows are mostly associated with marine sedimentary rocks. Includes acidic and intermediate volcanic rocks in northern Cascade Mountains.
Granite, quartz monzonite, quartz diorite, granodiorite, and trondhjemite. Includes diorite in southeastern Washington; diorite and gabbro near Concunully in Okanogan County; gneiss, schist, and migmatites in areas of Chelan, Colville, and Okanogan batholiths. Includes high-grade metamorphic rocks of Precambrian age in Spokane area.
Glacial and glaciofluvial sand, gravel, and till; includes alpine glacier outwash and till as well as some Recent alluvium.
Fine-grained sand and silt, well-stratified, with some gravel, clay, and diatomaceous earth. Contains clastic dikes in Walla Walla area.
Schist, gneiss, marble, quartzite, amphibolite, greenstone, metaconglomerate, graywacke; includes metasedimentary, volcanic, and intrusive rocks. Some areas, as on San Juan Islands, show little if any metamorphism.
Andesite and rhyodacite flows, tuff, and tuffaceous sandstones of northern Lincoln County and southwestern Stevens County.
Poorly to moderately consolidated tuffaceous sandstone, conglomerate, siltstone, and claystone in western Washington. Chiefly clay and shale with minor sand, gravel, and diatomaceous earth near Spokane. Includes diatomite beds near Yakima and Quincy, and some marine beds in Western Washington.
Advance and recessional outwash, stratified drift, and associated deposits. Primarily silt, sand, and gravel with some clay. Includes alluvium locally and scabland deposits of eastern Washington.
Gritstone with conglomerate in lower part and gray, white, and buff platy quartzite in upper part grading upward into phyllite; northern Pend Oreille County. Light-gray, platy, medium- to thick-bedded quartzite in upper part and darker impure quartzite with some interbedded argillite or phyllite in lower part; north-central Stevens County. White, gray, and reddish, medium- to thick-bedded quartzite in lower part and thin interbeds of quartzite and argillite in upper part, with very low Lower Cambrian fossils (Nevadia, Hyolthellus, and three genera of brachipods) near base of upper part; Addy district of central Stevens County. Thick argillite and thin quartzite units form an uppermost zone in southwestern Stevens County. Conspicuous phyllite units near base in north-central Lincoln County.
Predominantly a well-cemented, heterogeneous mixture of volcanic gravel, sand, silt, and clay. Contains some till and in western Washington is commonly deeply weathered.
Mostly massive dolomite, with a basal unit of gray to dark-gray limestone interbedded with limy shale, and an upper unit of fine-grained massive limestone with some marble; Pend Oreille and northern and central Stevens Counties. Three-fold division less evident in Colville area. Dolomite, with minor basal unit of interbedded limestone and phyllite in the Addy-Dunn Mountain area of Stevens County. Marble, dolomite, limestone, and limy slate in Hunters' district. Dolomitic marble in southern Stevens and northern Lincoln Counties. Middle Cambrian fossils near base in Metaline district, and Bathyuriscus-Elrathina fauna in lower unit in Leadpoint district. Phosphatic brachiopods in upper unit in Leadpoint district tentatively assigned to Middle and Upper Cambrian.