Geologic units in Humboldt county, California

Additional scientific data in this geographic area

Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 36 % 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.

Tertiary-Cretaceous Coastal Belt Rocks (Late Cretaceous to Pliocene) at surface, covers 15 % of this area

Sandstone, shale and minor conglomerate in coastal belt of northwestern California; included by some in Franciscan Complex. Previously considered Cretaceous, but now known to contain early Tertiary microfossils in places.

Franciscan schist (Early Cretaceous) at surface, covers 11 % of this area

Blueschist and semi-schist of Franciscan complex

Paleocene marine rocks, unit 2 (Northern California) (Paleocene to late Eocene) at surface, covers 8 % of this area

Sandstone, shale, and conglomerate; mostly well consolidated

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

Pliocene marine rocks (Miocene to Pleistocene) at surface, covers 6 % of this area

Sandstone, siltstone, shale, and conglomerate; in part Pleistocene and Miocene.

Quaternary alluvium and marine deposits (Pleistocene to Holocene) at surface, covers 4 % of this area

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

Mesozoic granitic rocks, unit 5 (Klamath Mountains) (Jurassic to early Cretaceous) at surface, covers 4 % of this area

Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite

Paleozoic marine rocks, undivided, unit 9 (Western Klamath Mountains) (Devonian to Jurassic) at surface, covers 3 % of this area

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

Older Quaternary alluvium and marine deposits (Pleistocene) at surface, covers 2 % of this area

Older alluvium, lake, playa, and terrace deposits.

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

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers 1.0 % of this area

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

Ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains) (Late Proterozoic(?) to Early Jurassic) at surface, covers 0.8 % of this area

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

Quaternary sand deposits, unit 1 (coastal) (Quaternary) at surface, covers 0.4 % of this area

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

Miocene marine rocks (Oligocene to Pliocene) at surface, covers 0.2 % of this area

Sandstone, shale, siltstone, conglomerate and breccia; in part Pliocene and Oligocene.

Tertiary intrusive rocks (hypabyssal), unit 8 (Crescent City) (Tertiary) at surface, covers < 0.1 % of this area

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

Mesozoic volcanic rocks, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers < 0.1 % 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.