Geologic units in Whatcom county, Washington

Additional scientific data in this geographic area

Tertiary granitic rocks (Probably mostly Eocene; ranges from Miocene to Paleocene) at surface, covers 11 % of this area

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

Pre-Upper Jurassic gneiss (Mostly Cretaceous) at surface, covers 11 % 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.

Cretaceous sedimentary rocks, mostly marine (Cretaceous) at surface, covers 10 % of this area

Lower Cretaceous greenish-gray massive arkosic sandstone and light-gray sandy shale in western Okanogan County. Includes phyllite in eastern Whatcom County.

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.

Paleocene-Cretaceous nonmarine rocks (Eocene (see age coding)) at surface, covers 9 % 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.

Younger glacial drift (Pleistocene) at surface, covers 7 % 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.

Younger glacial drift (Pleistocene) at surface, covers 6 % 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.

Carboniferous-Permian sedimentary and volcanic rocks (Devonian to Permian; some Jurassic) at surface, covers 5 % of this area

Sedimentary and volcanic rocks, undivided. Cherty and slaty argillite, siltstone, graywacke, chert, greenstone, tuff, andesite, and spilitic volcanics.

Pre-Upper Jurassic metamorphic rocks of the low-grade zone (Jurassic) at surface, covers 4 % of this area

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

Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks (Late Jurassic-Early Cretaceous) at surface, covers 4 % 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.

Carboniferous and Permian volcanic rocks (Devonian to Permian; Triassic in Asotin County) at surface, covers 4 % of this area

Predominantly altered andesite, basalt, and diabase with interbedded chert and argillite; includes some tuff, greenstone, and spilitic volcanic rocks; northern Cascade Mountains. Mostly schistose greenstone, some agglomerate, and rarely lapilli; includes minor beds of limestone with associated argillite and graywacke; northwestern Stevens County.

Pleistocene-Recent volcanic rocks (Pleistocene to Holocene) at surface, covers 4 % of this area

Predominantly dark-gray to black vesicular basalt; olivine-rich in part. Includes andesite flows and pyroclastic rocks of Mount Baker, Glacier Peak, Mount Rainier, Mount Adams, Mount St. Helens, and all cinder cones in southern part of the State. Also includes some Recent flows southeast of Mount St. Helens.

Carboniferous-Permian sedimentary and volcanic rocks (Devonian to Permian, minor Mesozoic) at surface, covers 3 % of this area

Predominantly sedimentary rocks. Graywacke, argillite, and slate; includes minor marble, siltstone, arkose, conglomerate, ribbon cherts, and volcanic rocks. Some Devonian rocks may be included in northwestern Washington.

Pre-Upper Jurassic metamorphic rocks of the low-grade zone (Early Cretaceous metamorphism (Jurassic protolith)) at surface, covers 3 % of this area

Greenschist of central Whatcom and Skagit Counties.

Glacial drift, undivided (Pleistocene) at surface, covers 2 % of this area

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

Miocene volcanic rocks (Middle Miocene) at surface, covers 1 % of this area

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.

Tertiary dunite intrusive rocks (Late Cretaceous) at surface, covers 1 % of this area

An intimate mixture of saxonite and dunite, partly serpentinized; Twin Sisters mountain area of Whatcom and Skagit Counties. Predominantly dunite and associated serpentinite in Jumbo Mountain area of central Snohomish County.

Pre-Tertiary sedimentary and metasedimentary rocks, undivided (Mostly Early Cretaceous to Middle Jurassic, possibly includes minor Eocene rocks) at surface, covers 1 % 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.

Younger glacial drift (Pleistocene) at surface, covers 0.8 % of this area

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

Pre-Upper Jurassic metamorphic rocks of the medium and high-grade zone (Early Jurassic-Triassic) at surface, covers 0.8 % of this area

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

Tertiary-Cretaceous granitic intrusive rocks (Early Tertiary-Late Cretaceous) at surface, covers 0.6 % of this area

Granite, granodiorite, trondhjemite, and quartz diorite. Late Cretaceous and/or early Tertiary.

Middle Jurassic volcanic rocks (Middle Jurassic) at surface, covers 0.4 % of this area

Andesite, dacite, and minor basalt with slate and graywacke interbeds in the Nooksack River region of Whatcom County.

Tertiary nonmarine rocks, undivided (Tertiary; mostly Eocene) at surface, covers 0.4 % of this area

Sandstone, shale, conglomerate, agglomerate, and tuff; includes some lava flows. Massive conglomerate, sandstone, siltstone, and ferruginous shale in northwestern Whatcom County.

Pre-Carboniferous crystalline complex (Devonian) at surface, covers 0.4 % of this area

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

Upper Triassic and/or Lower Jurassic Marine Rocks (Cretaceous-Triassic) at surface, covers 0.2 % of this area

Conglomerate, gritstone, graywacke, and carbonaceous argillite of northwestern Whatcom County.

Tertiary volcanic rocks, undivided (Mostly Oligocene-Eocene) at surface, covers 0.2 % of this area

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

Pre-Tertiary ultrabasic intrusive rocks (Late-Jurassic) at surface, covers 0.2 % of this area

Peridotite and pyroxenite; generally altered partly or completely to serpentine. Includes serpentinite and saxonite on Sumas Mountain, Whatcom County.

Lower and Middle Jurassic marine rocks (Devonian-Permian) at surface, covers 0.1 % of this area

Dark-gray, massive to thick-bedded, siliceous argillite, siltstone, and shale; includes minor graywacke and limestone. Confined to northwestern Whatcom 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.

Basic intrusive rocks, undivided (Jurassic in central Cascades; Oligocene to Eocene in northern Cascades) at surface, covers < 0.1 % of this area

Predominantly gabbro; includes some serpentine. Age undetermined.

Landslide and mudflow deposits (Holocene) at surface, covers < 0.1 % 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.

Cretaceous sedimentary rocks, mostly marine (Cretaceous) at surface, covers < 0.1 % of this area

Upper Cretaceous black siltstone, graywacke, and silica pebble conglomerate in western Okanogan County.

Upper Jurassic-Lower Cretaceous volcanic rocks (Jurassic-Cretaceous on San Juan Islands; possibly Eocene in King County) at surface, covers < 0.1 % of this area

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

Permian rocks (Permian-Triassic) at surface, covers < 0.1 % of this area

Conglomerate, graywacke, siltstone, argillite and interbedded fossiliferous limestone, greenstone, and minor angular conglomerate in northwestern Stevens and Ferry Counties. Impure quartzite, sandstone, graywacke, greenstone, ribbon chert, chert breccia, and limestone in Snohomish County and on San Juan Island. Lower Permian limestone on Black Mountain in northwestern Whatcom County. Middle Permian rocks in northeastern Washington.

Pre-Tertiary metamorphic rocks, undivided (Probably Permian) at surface, covers < 0.1 % of this 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.

Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks (Late Cretaceous-Jurassic) at surface, covers < 0.1 % of this area

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