Geologic units in King county, Washington

Additional scientific data in this geographic area

Oligocene-Miocene volcanic rocks (Miocene) at surface, covers 17 % of this area

Andesite flow breccia, andesite flows, and minor tuff beds; includes some basalt flows and flow breccia. Commonly more massive and less altered than similar-appearing Eocene-Oligocene volcanic rocks. Clastic flows and flows of black glass, and course to fine-grained clastic and pyroclastic rocks in the Republic and Curlew areas of Ferry County.

Younger glacial drift (Pleistocene) at surface, covers 15 % of this area

Till. Hard, blue-gray to gray concrete-like mixture of clay, silt, sand, and gravel deposited as end or recessional moraine. Principally Wisconsin in age.

Tertiary granitic rocks (Probably mostly Eocene; ranges from Miocene to Paleocene) at surface, covers 14 % of this area

Granite, quartz monzonite, quartz diorite, granodiorite, and trondhjemite. Includes dacite porphyry and granite breccia near Bumping Lake, Yakima County.

Younger glacial drift (Pleistocene) at surface, covers 10 % of this area

Younger glacial drift, undivided. Till, outwash, and associated deposits; sorted and unsorted sand, gravel, silt, and clay. Includes some alluvium.

Younger glacial drift (Pleistocene) at surface, covers 10 % of this area

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.

Alluvium (Holocene) at surface, covers 9 % of this area

Mostly unconsolidated silt, sand, and gravel valley fill with some clay; includes low-level terrace, marsh, peat, artificial fill, and glacial deposits locally.

Eocene volcanic rocks (Eocene) at surface, covers 4 % of this area

Predominantly andesite flows and breccia; includes interbedded sedimentary rocks south of Startup in Snohomish and King Counties.

Eocene-Oligocene volcanic rocks (Eocene-Oligocene) at surface, covers 3 % of this area

Predominantly light-green, bedded andesite breccia with interbedded andesite and basalt flows, mudflows, and tuff beds; becomes more tuffaceous near top of unit. Includes tuffaceous and arkosic sandstone, shale, and carbonaceous shale beds in central and southern Cascade Mountians. Rhyodacite and quartz latite flows in northwestern Ferry County.

Mesozoic granitic rocks, undivided (Mostly Cretaceous-Jurassic) at surface, covers 3 % of this area

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.

Older glacial drift (Pleistocene) at surface, covers 2 % of this area

Till, outwash, and associated interglacial deposits; sorted and unsorted gravel, sand, silt, and clay. Includes peat beds and non-glacial sediments locally. Mostly pre-Wisconsin in age.

Paleocene-Cretaceous nonmarine rocks (Eocene (see age coding)) at surface, covers 2 % of this area

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.

Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks (Late Jurassic-Early Cretaceous) at surface, covers 2 % of this area

Predominantly sedimentary rocks. Graywacke, argillite, and siltstone with some slate and phyllite; includes graywacke breccia and ribbon chert with minor local limestone lenses and basalt flows.

Landslide and mudflow deposits (Holocene) at surface, covers 2 % of this area

Predominantly landslide debris. Includes till-like mudflow deposits of andesitic rock fragments in clayey sand matrix in Buckley-Enumclaw area of Kind and Pierce Counties.

Upper Eocene volcanic rocks (Late Eocene) at surface, covers 2 % of this area

Predominantly andesite flows and breccia; includes some basalt flows. Contains basaltic conglomerate, pyroclastic rocks, tuff beds, and sandstone in Chehalis-Centralia coal district, Lewis County.

Upper upper Eocene nonmarine and marine rocks (Middle Eocene) at surface, covers 0.9 % of this area

Massive to thin-bedded, feldspathic to arkosic sandstone, siltstone, shale, and carbonaceous shale; becomes mostly marine in the western foothills of Cascade Mountains where coal beds are abundant. Basaltic sandstone and siltstone in northern Olympic Peninsula.

Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks (Late Cretaceous-Jurassic) at surface, covers 0.6 % of this area

Sedimentary and volcanic rocks, undivided. Graywacke, argillite, siltstone, slate, volcanic rocks, phyllite, greenschist, and greenstone.

Glacial drift, undivided (Pleistocene) at surface, covers 0.6 % of this area

Glacial and glaciofluvial sand, gravel, and till; includes alpine glacier outwash and till as well as some Recent alluvium.

Pre-Upper Jurassic metamorphic rocks of the low-grade zone (Jurassic) at surface, covers 0.5 % of this area

Greenschist, phyllite, and slate; includes some limestone, quartzose phyllite, schistose metaconglomerate, breccia, and basic igneous rocks. Includes schist locally.

Pre-Tertiary sedimentary and metasedimentary rocks, undivided (Mostly Early Cretaceous to Middle Jurassic, possibly includes minor Eocene rocks) at surface, covers 0.4 % of this area

Graywacke, argillite, phyllite, chert, talc, and graphite schist; some faulted-in blocks of serpentinite and greenstone. Includes minor limestone on San Juan Island.

Tertiary volcanic rocks, undivided (Mostly Oligocene-Eocene) at surface, covers 0.4 % of this area

Includes andesite, basalt, and rhyolite flows, and associated pyroclastic rocks. In isolated areas across the northern part of the State.

Pre-Middle Jurassic sedimentary and volcanic rocks (Late Paleozoic deposition? with Cretaceous metamorphism?) at surface, covers 0.3 % of this area

Sedimentary and volcanic rocks, undivided. Graywacke, argillite, slate, greenstone, and spilitic volcanic rocks.

Eocene nonmarine rocks (Eocene) at surface, covers 0.3 % of this area

Predominantly sandstone and shale. Includes some conglomerate in the Cle Elum area in Kittilas County. Contains extensive coal seams near Roslyn and carbonaceous shale and coal beds in White Pass area. Contains tuff beds in northwestern Ferry County.

Lower upper Eocene marine and nonmarine rocks (Eocene) at surface, covers 0.2 % of this area

Predominantly massive to well-bedded tuffaceous marine siltstone with interbedded arkosic and basaltic sandstone. Includes conglomerate in King County and along north side of Olympic Peninsula. Minor lava flows and breccia in western Lewis County and eastern Grays Harbor County. Coal seams in central Lewis County and north-central Pierce County.

Pre-Upper Jurassic gneiss (Mostly Cretaceous) at surface, covers 0.2 % of this 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.

Pre-Upper Jurassic metamorphic rocks of the medium and high-grade zone (Early Jurassic-Triassic) at surface, covers 0.2 % of this area

Schist, amphibolite, and minor lime-silicate rocks, marble, quartzite, and metaconglomerate.

Upper Jurassic-Lower Cretaceous volcanic rocks (Jurassic-Cretaceous on San Juan Islands; possibly Eocene in King County) at surface, covers 0.2 % of this area

Predominantly volcanic rocks, mostly metamorphosed to greenstone and greenschist; includes some sedimentary rocks

Oligocene marine rocks (Late Eocene to Late Oligocene) at surface, covers 0.1 % of this area

Massive, tuffaceous and nontuffaceous sandstone and siltstone; locally concretionary; includes conglomerate along the north coast of Olympic Peninsula and basaltic sandstone east of Chehalis.

Lower Tertiary volcanic rocks, undivided (Eocene) at surface, covers < 0.1 % of this area

Predominantly andesite flows and flow breccia; includes basalt flows, minor rhyolitic rocks, and some sedimentary rocks.

Mesozoic volcanic rocks, undivided (Jurassic) at surface, covers < 0.1 % of this area

Includes latite, andesite and basalt flows, tuff, and agglomerate. Interbedded sedimentary rocks in Orient area of Stevens County.

Tertiary dikes, sills, and small intrusive bodies (Middle to Late Tertiary) at surface, covers < 0.1 % of this area

Dikes are commonly diabase; plugs and sills are generally andesite porphyry and dacite.

Oligocene-Miocene marine rocks (Oligocene) at surface, covers < 0.1 % of this area

Massive to thin-bedded, coarse-grained sandstone, conglomerate, conglomeratic sandstone, shale, and sandy shale.

Upper Eocene volcanic rocks (Late Eocene) at surface, covers < 0.1 % of this area

Andesite and basalt flows and associated breccia in central Lewis County. Pyroclastic rocks, mudflows, flow breccia, and volcanic-rich sedimentary rocks in King and Pierce Counties.

Pre-Carboniferous crystalline complex (Devonian) at surface, covers < 0.1 % of this area

Metahornblendite, amphibolite, gneiss, metadiorite, meta-quartz diorite, and trondhjemite. As klippes along western slope of northern Cascade Mountains.

Miocene nonmarine rocks (Late Miocene) at surface, covers < 0.1 % of this area

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.

Pre-Middle Jurassic sedimentary and volcanic rocks (Jurassic) at surface, covers < 0.1 % of this area

Predominantly sedimentary rocks. Graywacke, argillite, and slate; includes minor marble, siltstone, arkose, conglomerate, ribbon cherts, and volcanic rocks.