Geologic units in Lassen county, California

Additional scientific data in this geographic area

Tertiary volcanic flow rocks, unit 17 (Cascade Range) (Tertiary (2-24 Ma)) at surface, covers 44 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Quaternary volcanic flow rocks, unit 1 (Cascade Volcanic Field) (Quaternary) at surface, covers 21 % of this area

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

Quaternary alluvium and marine deposits (Pliocene to Holocene) at surface, covers 20 % of this area

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

Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range) (Tertiary (2-24 Ma)) at surface, covers 6 % of this area

Tertiary pyroclastic and volcanic mudflow deposits.

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers 4 % of this area

Pliocene and/or Pleistocene sandstone, shale, and gravel deposits; in part Miocene.

Quaternary sand deposits, unit 2 (inland) (Quaternary) at surface, covers 1 % of this area

Extensive marine and nonmarine sand deposits, generally near the coast or desert playas

Recent (Holocene) volcanic flow rocks, unit 1 (Cascade Volcanic Field) (Holocene) at surface, covers 0.6 % of this area

Recent (Holocene) volcanic flow rocks; minor pyroclastic deposits; in part Pleistocene.

Lithology: andesite; dacite

Undivided pre-Cenozoic metavolcanic rocks, unit 2 (undivided) (Paleozoic(?) to Mesozoic(?)) at surface, covers 0.5 % of this area

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

Eocene nonmarine rocks, unit 1 (Northern and Central California) (Eocene) at surface, covers 0.5 % of this area

Sandstone, shale, and conglomerate.

Tertiary intrusive rocks (hypabyssal), unit 1 (Cascades Volcanic Field) (Tertiary) at surface, covers 0.2 % of this area

Tertiary intrusive rocks; mostly shallow (hypabyssal) plugs and dikes. Includes some Mesozoic rocks.

Mesozoic volcanic rocks, unit 5 (Northern Sierra Nevada and Eastern Klamath Mountains) (Late Permian(?) to Jurassic) at surface, covers 0.2 % 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

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

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

Lithology: glacial drift

Jurassic marine rocks, unit 5 (Northern Sierra Nevada and Eastern Klamath Mountains) (Devonian to Late Jurassic) at surface, covers < 0.1 % of this area

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

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.

Basalt flows (Late Miocene to Middle Miocene) at surface, covers < 0.1 % of this area

BASALT FLOWS

Lithology: basalt

Playa, marsh, and alluvial-flat deposits, locally eroded (Quaternary) at surface, covers < 0.1 % of this area

PLAYA, MARSH, AND ALLUVIAL-FLAT DEPOSITS, LOCALLY ERODED

Lithology: playa; alluvium

Ash-flow tuffs and tuffaceous sedimentary rocks (Middle Miocene to Late Miocene) at surface, covers < 0.1 % of this area

ASH-FLOW TUFFS AND TUFFACEOUS SEDIMENTARY ROCKS

Granitic rocks (Cretaceous) at surface, covers < 0.1 % of this area

GRANITIC ROCKS-Mostly quartz monzonite and granodiorite

Alluvial deposits (Quaternary) at surface, covers < 0.1 % of this area

ALLUVIAL DEPOSITS-Locally includes beach and sand dune deposits