Geologic units in Sonoma county, California

Franciscan melange (Jurassic to Cretaceous) at surface, covers 20 % of this area

Melange of fragmented and sheared Franciscan complex rocks.

Tertiary-Cretaceous Coastal Belt Rocks (Late Cretaceous to Pliocene) at surface, covers 17 % 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.

Quaternary alluvium and marine deposits (Pleistocene to Holocene) at surface, covers 12 % of this area

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

Tertiary volcanic flow rocks, unit 3 (Sonoma Volcanic Field) (Tertiary (3-7 Ma)) at surface, covers 10 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Pliocene marine rocks (Miocene to Pleistocene) at surface, covers 8 % of this area

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

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers 7 % 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 5 % of this area

Older alluvium, lake, playa, and terrace deposits.

Mesozoic volcanic rocks, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 4 % 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.

Lower Cretaceous marine rocks (Early Cretaceous) at surface, covers 4 % of this area

Lower Cretaceous sandstone, shale, and conglomerate

Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers 3 % 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.

Franciscan schist (Early Cretaceous) at surface, covers 3 % of this area

Blueschist and semi-schist of Franciscan complex

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

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

Tertiary pyroclastic and volcanic mudflow deposits, unit 1 (Sonoma Volcanic Field) (Tertiary (3-7 Ma)) at surface, covers 2 % of this area

Tertiary pyroclastic and volcanic mudflow deposits.

Eocene and Paleocene marine rocks, undivided (Paleocene to middle Eocene) at surface, covers 1 % of this area

Eocene and Paleocene marine rocks, undivided

Upper Cretaceous marine rocks, unit 1 (Upper Great Valley Sequence) (Late Cretaceous) at surface, covers 0.4 % of this area

Upper Cretaceous sandstone, shale, and conglomerate

Mesozoic gabbroic rocks, unit 2 (undivided) (Triassic to Cretaceous) at surface, covers 0.4 % of this area

Gabbro and dark dioritic rocks; chiefly Mesozoic

Quaternary large landslide deposits (Quaternary) at surface, covers 0.3 % of this area

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

Paleocene marine rocks, unit 1 (Central and Southern California) (Paleocene) at surface, covers 0.3 % of this area

Sandstone, shale, and conglomerate; mostly well consolidated

Tertiary volcanic flow rocks, unit 1 (Quien Sabe-Burdell Mountain) (Tertiary (9.5-13 Ma)) at surface, covers 0.2 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

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

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

Quaternary sand deposits, unit 1 (coastal) (Quaternary) at surface, covers < 0.1 % of this area

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

Jurassic marine rocks, unit 2 (Coast Ranges) (Late Jurassic to Early Cretaceous) at surface, covers < 0.1 % of this area

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

Quaternary volcanic flow rocks, unit 3 (Clear Lake Volcanic Field) (Quaternary (0-4 Ma)) at surface, covers < 0.1 % of this area

Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.

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