Geologic units in Contra Costa county, California

Quaternary alluvium and marine deposits (Pleistocene to Holocene) at surface, covers 24 % of this area

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

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers 18 % of this area

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

Miocene marine rocks (Oligocene to Pliocene) at surface, covers 15 % of this area

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

Upper Cretaceous marine rocks, unit 1 (Upper Great Valley Sequence) (Late Cretaceous) at surface, covers 14 % of this area

Upper Cretaceous sandstone, shale, and conglomerate

Older Quaternary alluvium and marine deposits (Pleistocene) at surface, covers 9 % of this area

Older alluvium, lake, playa, and terrace deposits.

Eocene marine rocks (Paleocene to Oligocene) at surface, covers 9 % of this area

Shale, sandstone, conglomerate, and minor limestone; in part Oligocene and Paleocene.

Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 2 % 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.

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

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

Lower Cretaceous marine rocks (Early Cretaceous) at surface, covers 2 % of this area

Lower Cretaceous sandstone, shale, and conglomerate

Paleocene marine rocks, unit 1 (Central and Southern California) (Paleocene) at surface, covers 2 % of this area

Sandstone, shale, and conglomerate; mostly well consolidated

Tertiary volcanic flow rocks, unit 4 (Berkeley Hills) (Tertiary (8-12 Ma)) at surface, covers 0.9 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Cretaceous marine rocks (in part nonmarine), unit 1 (Coast Ranges) (Early to Late Cretaceous) at surface, covers 0.8 % of this area

Undivided Cretaceous sandstone, shale, and conglomerate; minor nonmarine rocks in Peninsular Ranges

Mesozoic volcanic rocks, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 0.6 % 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.

Oligocene marine rocks (Eocene to Miocene) at surface, covers 0.6 % of this area

Sandstone, shale, and conglomerate; in part Miocene and Eocene.

Jurassic marine rocks, unit 2 (Coast Ranges) (Late Jurassic to Early Cretaceous) at surface, covers 0.4 % of this area

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

Ultramafic rocks, chiefly Mesozoic, unit 3 (Coast Ranges and Western Klamath Mountains) (Middle to Late Jurassic) at surface, covers 0.3 % of this area

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

Tertiary pyroclastic and volcanic mudflow deposits, unit 2 (Berkeley Hills) (Tertiary (8-12 Ma)) at surface, covers 0.3 % of this area

Tertiary pyroclastic and volcanic mudflow deposits.

Tertiary intrusive rocks (hypabyssal), unit 9 (Jurassic gabbros along Hayward Fault) (Jurassic) at surface, covers < 0.1 % of this area

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