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.
Biotite, quartz diorite, trondhjemite, and hornblende gneisses, many of which are migmatitic; includes small granitic bodies locally. Small areas of mica schist, marble, amphibolite, and lime-silicate rocks in Entiat Mountains area of Chelan County.
Brown-gray to light-gray, medium- to course-grained massive cross-bedded arkose with interbedded conglomerate and siltstone. Contains several coal seams in Whatcom County. Iron-rich laterite at base near Cle Elum and Blewett Pass in Kittitas and Chelan Counties.
Schist, amphibolite, and minor lime-silicate rocks, marble, quartzite, and metaconglomerate.
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.
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.
Granite, quartz monzonite, quartz diorite, granodiorite, and trondhjemite. Includes dacite porphyry and granite breccia near Bumping Lake, Yakima County.
Mostly unconsolidated silt, sand, and gravel valley fill with some clay; includes low-level terrace, marsh, peat, artificial fill, and glacial deposits locally.
Peridotite and pyroxenite; generally altered partly or completely to serpentine. Includes serpentinite and saxonite on Sumas Mountain, Whatcom County.
Glacial and glaciofluvial sand, gravel, and till; includes alpine glacier outwash and till as well as some Recent alluvium.
Granite, granodiorite, trondhjemite, and quartz diorite. Late Cretaceous and/or early Tertiary.
Younger glacial drift, undivided. Till, outwash, and associated deposits; sorted and unsorted sand, gravel, silt, and clay. Includes some alluvium.
Predominantly gabbro; includes some serpentine. Age undetermined.
Meta-quartz diorite, hypersthene diorite, and gneissose and directionless quartz diorite of eastern Skagit County. Quartz diorite and diorite in the San Juan Islands. Includes amphibolite and gneiss locally.
Predominantly greenstone and spilitic volcanic rocks; includes some slate, argillite, and graywacke.
Includes andesite, basalt, and rhyolite flows, and associated pyroclastic rocks. In isolated areas across the northern part of the State.
Greenschist, phyllite, and slate; includes some limestone, quartzose phyllite, schistose metaconglomerate, breccia, and basic igneous rocks. Includes schist locally.
Dikes are commonly diabase; plugs and sills are generally andesite porphyry and dacite.
Unconsolidated to partly consolidated fluvial and glaciofluvial sand and gravel with minor amounts of silt and clay. Includes marine terrace along west coast of the Olympic Peninsula.
Dark-gray, fine-grained, dense, porphyritic in part, basalt flows in central and south-central part of State; commonly interbedded with conglomerate, sandstone, and siltstone. Includes small areas of rhyolite north of Cle Elum in Kittitas County, and andesite north of Leavenworth in Chelan County.
Andesite and basalt flows, and greenstone; includes minor interbedded limestone, arkose, quartzite, and chert beds.