Skip to main content

Geologic units in Tehama county, California

Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range) (Tertiary (2-24 Ma)) at surface, covers 32 % of this area

Tertiary pyroclastic and volcanic mudflow deposits.

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers 26 % of this area

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

Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 11 % of this area

Franciscan complex: Cretaceous and Jurassic sandstone with smaller amounts of shale, chert, limestone, and conglomerate. Includes Franciscan melange, except where separated--see KJfm.

Lower Cretaceous marine rocks (Early Cretaceous) at surface, covers 11 % of this area

Lower Cretaceous sandstone, shale, and conglomerate

Quaternary volcanic flow rocks, unit 1 (Cascade Volcanic Field) (Quaternary) at surface, covers 5 % of this area

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

Tertiary volcanic flow rocks, unit 17 (Cascade Range) (Tertiary (2-24 Ma)) at surface, covers 4 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Upper Cretaceous marine rocks, unit 1 (Upper Great Valley Sequence) (Late Cretaceous) at surface, covers 2 % of this area

Upper Cretaceous sandstone, shale, and conglomerate

Jurassic marine rocks, unit 2 (Coast Ranges) (Late Jurassic to Early Cretaceous) at surface, covers 2 % of this area

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

Paleozoic marine rocks, undivided, unit 9 (Western Klamath Mountains) (Devonian to Jurassic) at surface, covers 2 % of this area

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

Ultramafic rocks, chiefly Mesozoic, unit 3 (Coast Ranges and Western Klamath Mountains) (Middle to Late Jurassic) at surface, covers 2 % of this area

Ultramafic rocks, mostly serpentine. Minor peridotite, gabbro, and diabase. Chiefly Mesozoic unit 3

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

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

Lithology: andesite; dacite

Mesozoic volcanic rocks, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 0.8 % 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

Ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains) (Late Proterozoic(?) to Early Jurassic) at surface, covers 0.7 % of this area

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

Quaternary glacial deposits (Pleistocene) at surface, covers 0.2 % of this area

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

Lithology: glacial drift

Mesozoic gabbroic rocks, unit 2 (undivided) (Triassic to Cretaceous) at surface, covers 0.2 % of this area

Gabbro and dark dioritic rocks; chiefly Mesozoic

Lithology: gabbro; diorite

Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains) (Triassic to Late Jurassic) at surface, covers 0.1 % of this area

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

Quaternary alluvium and marine deposits (Pliocene to Holocene) at surface, covers 0.1 % of this area

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

Undated granitic rocks, unit 2 (Western Klamath Mountains) (Late Triassic to Early Jurassic) at surface, covers < 0.1 % of this area

Undated granitic rocks unit 2

pre-Cenozoic metasedimentary and metavolcanic rocks undivided (Early Proterozoic to Cretaceous) at surface, covers < 0.1 % 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.

Tertiary volcanic flow rocks, unit 19 (Lovejoy) (Tertiary (14-16 Ma)) at surface, covers < 0.1 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Lithology: basalt

Franciscan schist (Early Cretaceous) at surface, covers < 0.1 % of this area

Blueschist and semi-schist of Franciscan complex

Tertiary intrusive rocks (hypabyssal), unit 1 (Cascades Volcanic Field) (Tertiary) at surface, covers < 0.1 % of this area

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