Geologic units in San Francisco county, California

Quaternary sand deposits, unit 1 (coastal) (Quaternary) at surface, covers 40 % of this area

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

Quaternary alluvium and marine deposits (Pleistocene to Holocene) at surface, covers 28 % of this area

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

Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 21 % 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.

Ultramafic rocks, chiefly Mesozoic, unit 3 (Coast Ranges and Western Klamath Mountains) (Middle to Late Jurassic) at surface, covers 7 % of this area

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

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

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

Franciscan melange (Jurassic to Cretaceous) at surface, covers 0.4 % of this area

Melange of fragmented and sheared Franciscan complex rocks.

Mesozoic granitic rocks, unit 1 (Salinian Block) (Early to Late Cretaceous) at surface, covers < 0.1 % of this area

Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite

Pliocene marine rocks (Miocene to Pleistocene) at surface, covers < 0.1 % of this area

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