Geologic units in El Dorado county, California

Additional scientific data in this geographic area

Mesozoic granitic rocks, unit 3 (Sierra Nevada, Death Valley area, Northern Mojave Desert and Transverse Ranges) (Permian to Tertiary; most Mesozoic) at surface, covers 35 % of this area

Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite

Paleozoic marine rocks, undivided, unit 4 (Western Sierra Nevada) (Ordovician to Triassic) at surface, covers 19 % of this area

Undivided Paleozoic metasedimentary rocks. Includes slate, sandstone, shale, chert, conglomerate, limestone, dolomite, marble, phyllite, schist, hornfels, and quartzite

Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range) (Tertiary (2-24 Ma)) at surface, covers 15 % of this area

Tertiary pyroclastic and volcanic mudflow deposits.

Mesozoic volcanic rocks, unit 2 (Western Sierra Foothills and Western Klamath Mountains) (Jurassic) at surface, covers 9 % of this area

Undivided Mesozoic volcanic and metavolcanic rocks. Andesite and rhyolite flow rocks, greenstone, volcanic breccia and other pyroclastic rocks; in part strongly metamorphosed. Includes volcanic rocks of Franciscan Complex: basaltic pillow lava, diabase, greenstone, and minor pyroclastic rocks.

Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains) (Triassic to Late Jurassic) at surface, covers 7 % of this area

Shale, sandstone, minor conglomerate, chert, slate, limestone; minor pyroclastic rocks

Quaternary glacial deposits (Pleistocene) at surface, covers 5 % of this area

Glacial till and moraines. Found at high elevations mostly in the Sierra Nevada and Klamath Mountains.

Mesozoic gabbroic rocks, unit 2 (undivided) (Triassic to Cretaceous) at surface, covers 3 % of this area

Gabbro and dark dioritic rocks; chiefly Mesozoic

Ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains) (Late Proterozoic(?) to Early Jurassic) at surface, covers 2 % of this area

Ultramafic rocks, mostly serpentine. Minor peridotite, gabbro, and diabase. Chiefly Mesozoic unit 2

pre-Cenozoic metasedimentary and metavolcanic rocks undivided (Early Proterozoic to Cretaceous) at surface, covers 2 % of this area

Undivided pre-Cenozoic metasedimentary and metavolcanic rocks of great variety. Mostly slate, quartzite, hornfels, chert, phyllite, mylonite, schist, gneiss, and minor marble.

Jurassic marine rocks, unit 5 (Northern Sierra Nevada and Eastern Klamath Mountains) (Devonian to Late Jurassic) at surface, covers 1 % of this area

Shale, sandstone, minor conglomerate, chert, slate, limestone; minor pyroclastic rocks

Quaternary alluvium and marine deposits (Pleistocene to Holocene) at surface, covers 0.7 % of this area

Alluvium, lake, playa, and terrace deposits; unconsolidated and semi-consolidated. Mostly nonmarine, but includes marine deposits near the coast.

Undivided pre-Cenozoic metavolcanic rocks, unit 2 (undivided) (Paleozoic(?) to Mesozoic(?)) at surface, covers 0.4 % of this area

Undivided pre-Cenozoic metavolcanic rocks. Includes latite, dacite, tuff, and greenstone; commonly schistose.

Mesozoic volcanic rocks, unit 5 (Northern Sierra Nevada and Eastern Klamath Mountains) (Late Permian(?) to Jurassic) at surface, covers 0.4 % of this area

Undivided Mesozoic volcanic and metavolcanic rocks. Andesite and rhyolite flow rocks, greenstone, volcanic breccia and other pyroclastic rocks; in part strongly metamorphosed. Includes volcanic rocks of Franciscan Complex: basaltic pillow lava, diabase, greenstone, and minor pyroclastic rocks.

Paleozoic metavolcanic rocks, unit 4 (Western Sierra Nevada Foothills) (Paleozoic or Mesozoic) at surface, covers 0.2 % of this area

Undivided Paleozoic metavolcanic rocks. Mostly flows, breccia and tuff, including greenstone, diabase, and pillow lavas; minor interbedded sedimentary rocks

Quaternary volcanic flow rocks, unit 1 (Cascade Volcanic Field) (Quaternary) at surface, covers 0.2 % of this area

Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.

Tertiary nonmarine rocks, undivided (Paleocene to Pliocene) at surface, covers 0.1 % of this area

Undivided Tertiary sandstone, shale, conglomerate, breccia, and ancient lake deposits.

Felsic phaneritic intrusive rocks (Cretaceous) at surface, covers < 0.1 % of this area

Granodiorite, granite, and related rocks make up the largest group of granitic intrusions exposed in Nevada. They are present in every county, and are especially abundant in west-central Nevada in an arcuate belt along the border with California extending north and eastward towards Idaho.

Alluvium, undifferentiated (Holocene and Pleistocene) at surface, covers < 0.1 % of this area

Unit is present in all counties. Some counties divided the alluvium into younger and older units, and some did not. For those that did not, or used other generalized terms for Quaternary rocks, the unit Qal has been used for the general undivided alluvium. Additionally, when polygons have been edited and changed to alluvium, Qal was used as the general value; hence it now is present in all counties. Qya-Younger alluvium: Map unit is used in Churchill, Elko, Esmeralda, Eureka, Humboldt, Lander, and Lincoln Counties where geologic information suggests better-defined younger versus older alluvium. It is mostly interchangeable with Qal, except that it implies some specifically younger Quaternary deposits.