Geologic units in Okanogan county, Washington

Additional scientific data in this geographic area

Mesozoic granitic rocks, undivided (Mostly Cretaceous-Jurassic) at surface, covers 49 % 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.

Glacial drift, undivided (Pleistocene) at surface, covers 12 % of this area

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

Cretaceous sedimentary rocks, mostly marine (Cretaceous) at surface, covers 5 % 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.

Cretaceous sedimentary rocks, mostly marine (Cretaceous) at surface, covers 4 % of this area

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

Pre-Tertiary metamorphic rocks, undivided (Probably Permian) at surface, covers 4 % 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 3 % of this area

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

Pre-Upper Jurassic metamorphic rocks of the medium and high-grade zone (Early Jurassic-Triassic) at surface, covers 3 % of this area

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

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.

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.

Miocene volcanic rocks (Middle Miocene) at surface, covers 2 % 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-Upper Jurassic gneiss (Mostly Cretaceous) at surface, covers 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.

Tertiary volcanic rocks, undivided (Mostly Oligocene-Eocene) at surface, covers 1 % of this area

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

Upper Cretaceous-lower Tertiary volcanic rocks (Late Cretaceous) at surface, covers 1 % of this area

Dark-gray to green andesite tuff, breccia, and flows in Methow River area of Okanogan County.

Alluvium (Holocene) at surface, covers 1 % 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-Upper Jurassic metamorphic rocks of the low-grade zone (Jurassic) at surface, covers 1 % of this area

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

Tertiary-Cretaceous granitic intrusive rocks (Early Tertiary-Late Cretaceous) at surface, covers 0.7 % of this area

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

Triassic sedimentary rocks, undivided (Triassic with Permian where impossible to differentiate) at surface, covers 0.6 % of this area

Predominantly limestone, marble, and dolomite near Riverside in Okanogan County. Conglomerate, shale, graywacke, gritstone, and limestone on San Juan Island. Siltstone with greenstone locally on Orcas Island. Graywacke conglomerate, cherty greenstone, and limestone in northern Ferry County.

Upper Paleozoic rocks, undivided (Ordovician) at surface, covers 0.6 % of this area

Mostly graywacke, interbedded quartzite and phyllite, greenstone and serpentine, and black shale with minor limestone. Some quartz-mica schist in Bald Knob area of Ferry County. Schist, gneiss, and amphibolite in other parts of Ferry County. Some rocks of lower Paleozoic age, possibly Precambrian, and Mesozoic may be included.

Mesozoic volcanic rocks, undivided (Jurassic) at surface, covers 0.6 % of this area

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

Glaciolacustrine deposits (Pleistocene) at surface, covers 0.5 % of this area

Fine-grained sand and silt, well-stratified, with some gravel, clay, and diatomaceous earth. Contains clastic dikes in Walla Walla area.

Cretaceous nonmarine rocks (Late Cretaceous) at surface, covers 0.4 % of this area

Redbeds of thick-bedded sandstone, shale, and pebble conglomerate in upper Methow River area of Okanogan 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-Tertiary basic intrusive rocks (Triassic-Permian) at surface, covers 0.3 % of this area

Predominantly gabbro and metagabbro; includes hornblendite, peridotite, and pyroxenite. In Nighthawk district and near 49th Parallel in Okanogan County and in Orient district of Stevens County.

Tertiary dikes, sills, and small intrusive bodies (Middle to Late Tertiary) at surface, covers 0.2 % of this area

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

Pleistocene-Recent volcanic rocks (Pleistocene to Holocene) at surface, covers 0.2 % 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.

Mesozoic alkali intrusive rocks (Jurassic-Cretaceous) at surface, covers 0.2 % of this area

Syenite in Nighthawk and Buckhorn Mountain areas of Okanogan County; malignite on Kruger Mountain near Nighthawk.

Carboniferous and Permian volcanic rocks (Devonian to Permian; Triassic in Asotin County) at surface, covers 0.1 % 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.

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.

Paleocene-Cretaceous nonmarine rocks (Eocene (see age coding)) at surface, covers 0.1 % 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-Tertiary ultrabasic intrusive rocks (Late-Jurassic) at surface, covers < 0.1 % of this area

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

Lower Paleozoic rocks, undivided (Paleozoic; likely Ordovician) at surface, covers < 0.1 % of this area

Predominantly gneiss and schist in northern Ferry County. Quartzite, partly interbedded with dolomitic and calcitic marble, lime-silicate gneiss, and amphibolite; including in places forsterite marblean diopside marble, quartz-biotite-sillimanite schist and sillimanite-orthoclase gneiss in northeastern Ferry County. Quartzite with overlying limestone in southeastern Stevens County. Some upper Paleozoic and Precambrian rocks may be included.