Geologic units in Chelan county, Washington

Additional scientific data in this geographic area

Mesozoic granitic rocks, undivided (Mostly Cretaceous-Jurassic) at surface, covers 35 % 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.

Pre-Upper Jurassic gneiss (Mostly Cretaceous) at surface, covers 26 % 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.

Paleocene-Cretaceous nonmarine rocks (Eocene (see age coding)) at surface, covers 13 % 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.

Pre-Upper Jurassic metamorphic rocks of the medium and high-grade zone (Early Jurassic-Triassic) at surface, covers 9 % of this area

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

Miocene volcanic rocks (Middle Miocene) at surface, covers 3 % 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.

Pre-Tertiary metamorphic rocks, undivided (Probably Permian) at surface, covers 3 % 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.

Tertiary granitic rocks (Probably mostly Eocene; ranges from Miocene to Paleocene) at surface, covers 2 % of this area

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

Alluvium (Holocene) at surface, covers 2 % 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.

Pre-Tertiary ultrabasic intrusive rocks (Late-Jurassic) at surface, covers 2 % of this area

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

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.

Tertiary-Cretaceous granitic intrusive rocks (Early Tertiary-Late Cretaceous) at surface, covers 2 % of this area

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

Younger glacial drift (Pleistocene) at surface, covers 1 % of this area

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

Basic intrusive rocks, undivided (Jurassic in central Cascades; Oligocene to Eocene in northern Cascades) at surface, covers 0.4 % of this area

Predominantly gabbro; includes some serpentine. Age undetermined.

Pre-Carboniferous intrusive rocks (Paleozoic) at surface, covers 0.2 % of this area

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.

Pre-Middle Jurassic volcanic rocks, undivided (Early Cretaceous-Late Jurassic) at surface, covers 0.2 % of this area

Predominantly greenstone and spilitic volcanic rocks; includes some slate, argillite, and graywacke.

Tertiary volcanic rocks, undivided (Mostly Oligocene-Eocene) at surface, covers 0.1 % of this area

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

Pre-Upper Jurassic metamorphic rocks of the low-grade zone (Jurassic) at surface, covers 0.1 % of this area

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

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.

Terrace deposits (Pleistocene) at surface, covers < 0.1 % of this area

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.

Miocene-Pliocene volcanic rocks (Miocene-Pliocene) at surface, covers < 0.1 % of this area

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.

Pre-Tertiary volcanic rocks, undivided (Probably mostly Jurassic) at surface, covers < 0.1 % of this area

Andesite and basalt flows, and greenstone; includes minor interbedded limestone, arkose, quartzite, and chert beds.