Geologic units in Marin county, California

Additional scientific data in this geographic area

Franciscan melange (Jurassic to Cretaceous) at surface, covers 39 % of this area

Melange of fragmented and sheared Franciscan complex rocks.

Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 16 % 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.

Pliocene marine rocks (Miocene to Pleistocene) at surface, covers 11 % of this area

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

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

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

Miocene marine rocks (Oligocene to Pliocene) at surface, covers 7 % of this area

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

Franciscan schist (Early Cretaceous) at surface, covers 5 % of this area

Blueschist and semi-schist of Franciscan complex

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

Mesozoic volcanic rocks, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 3 % 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 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

Quaternary large landslide deposits (Quaternary) at surface, covers 1.0 % of this area

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

Quaternary sand deposits, unit 1 (coastal) (Quaternary) at surface, covers 0.7 % of this area

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

Tertiary volcanic flow rocks, unit 1 (Quien Sabe-Burdell Mountain) (Tertiary (9.5-13 Ma)) at surface, covers 0.7 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Lower Cretaceous marine rocks (Early Cretaceous) at surface, covers 0.5 % of this area

Lower Cretaceous sandstone, shale, and conglomerate

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers 0.3 % of this area

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

Older Quaternary alluvium and marine deposits (Pleistocene) at surface, covers 0.2 % of this area

Older alluvium, lake, playa, and terrace 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