Geologic units in San Luis Obispo county, California

Miocene marine rocks (Oligocene to Pliocene) at surface, covers 24 % of this area

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

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers 24 % of this area

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

Quaternary alluvium and marine deposits (Pleistocene to Holocene) at surface, covers 13 % 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 10 % 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.

Paleocene marine rocks, unit 3 (La Panza Range) (Late Cretaceous(?) to Eocene(?)) at surface, covers 6 % of this area

Sandstone, shale, and conglomerate; mostly well consolidated

Upper Cretaceous marine rocks, unit 1 (Upper Great Valley Sequence) (Late Cretaceous) at surface, covers 5 % of this area

Upper Cretaceous sandstone, shale, and conglomerate

Mesozoic granitic rocks, unit 1 (Salinian Block) (Early to Late Cretaceous) at surface, covers 4 % of this area

Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite

Upper Cretaceous and Paleocene marine rocks, undivided (Late Cretaceous to Paleocene) at surface, covers 3 % of this area

Sandstone, shale, and conglomerate

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

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

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

Older alluvium, lake, playa, and terrace deposits.

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

Lower Cretaceous sandstone, shale, and conglomerate

Ultramafic rocks, chiefly Mesozoic, unit 3 (Coast Ranges and Western Klamath Mountains) (Middle to Late Jurassic) at surface, covers 1 % of this area

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

Oligocene nonmarine rocks, unit 2 (Central and Southern California) (middle Eocene to early Miocene) at surface, covers 1 % of this area

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

Mesozoic volcanic rocks, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 1.0 % 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.

Pliocene marine rocks (Miocene to Pleistocene) at surface, covers 0.7 % of this area

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

Tertiary volcanic flow rocks, unit 14 (Tranquillon-Obispo) (Tertiary (16-18 Ma)) at surface, covers 0.7 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Miocene nonmarine rocks (Oligocene to Pleistocene) at surface, covers 0.6 % of this area

Sandstone, shale, conglomerate, and fanglomerate; in part Pliocene and Oligocene.

Tertiary volcanic flow rocks, unit 9 (Caliente) (Tertiary (14-18 Ma)) at surface, covers 0.4 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Tertiary pyroclastic and volcanic mudflow deposits, unit 4 (Tranquillon-Obispo) (Tertiary (16-18 Ma)) at surface, covers 0.4 % of this area

Tertiary pyroclastic and volcanic mudflow deposits.

Jurassic marine rocks, unit 2 (Coast Ranges) (Late Jurassic to Early Cretaceous) at surface, covers 0.3 % of this area

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

Franciscan melange (Jurassic to Cretaceous) at surface, covers 0.2 % of this area

Melange of fragmented and sheared Franciscan complex rocks.

Eocene marine rocks (Paleocene to Oligocene) at surface, covers 0.2 % of this area

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

Cretaceous marine rocks (in part nonmarine), unit 1 (Coast Ranges) (Early to Late Cretaceous) at surface, covers 0.2 % of this area

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

Tertiary intrusive rocks (hypabyssal), unit 4 (Tranquillon-Obispo) (Tertiary) at surface, covers 0.1 % of this area

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

Quaternary large landslide deposits (Quaternary) at surface, covers 0.1 % of this area

Selected large landslides, such as Blackhawk slide on north side of San Gabriel Mountains; early to late Quaternary.

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.

Paleocene marine rocks, unit 1 (Central and Southern California) (Paleocene) at surface, covers < 0.1 % of this area

Sandstone, shale, and conglomerate; mostly well consolidated

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.