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Geologic units in Imperial county, California

Additional scientific data in this geographic area

Quaternary alluvium and marine deposits (Pliocene to Holocene) at surface, covers 65 % of this area

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

Quaternary sand deposits, unit 2 (inland) (Quaternary) at surface, covers 7 % of this area

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

Tertiary volcanic flow rocks, unit 15 (Southern Mojave Desert) (Tertiary (8-28 Ma)) at surface, covers 4 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Tertiary nonmarine rocks, undivided (Paleocene to Pliocene) at surface, covers 3 % of this area

Undivided Tertiary sandstone, shale, conglomerate, breccia, and ancient lake deposits.

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers 2 % of this area

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

Precambrian igneous and metamorphic rock complex (Early Proterozoic to Miocene) at surface, covers 2 % of this area

Complex of Precambrian igneous and metamorphic rocks. Mostly gneiss and schist intruded by igneous rocks; may be Mesozoic in part.

Mesozoic granitic rocks , unit 2 (Peninsular Ranges) (Middle Jurassic to Late Cretaceous) at surface, covers 2 % of this area

Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite

Schist of various types and ages, unit 2 (Southern and West-central California) (Late Cretaceous to Eocene) at surface, covers 1 % of this area

Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.

Pliocene marine rocks (Miocene to Pleistocene) at surface, covers 1 % of this area

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

Undated granitic rocks, unit 1 (Chocolate Mountains) (Oligocene to Miocene) at surface, covers 0.9 % of this area

Undated granitic rocks unit 1

Tertiary pyroclastic and volcanic mudflow deposits, unit 7 (Southern Mojave Desert) (Tertiary (8-28 Ma)) at surface, covers 0.8 % of this area

Tertiary pyroclastic and volcanic mudflow deposits.

Precambrian rocks, undivided, unit 2 (Mojave Desert and Transverse Ranges) (Early Proterozoic to Miocene) at surface, covers 0.6 % of this area

Conglomerate, shale, sandstone, limestone, dolomite, marble, gneiss, hornfels, and quartzite; may be Paleozoic in part

pre-Cenozoic granitic and metamorphic rocks undivided (Early Proterozoic to Late Cretaceous) at surface, covers 0.5 % of this area

Granitic and metamorphic rocks, mostly gneiss and other metamorphic rocks injected by granitic rocks. Mesozoic to Precambrian.

Tertiary intrusive rocks (hypabyssal), unit 6 (Southern Mojave Desert) (Tertiary) at surface, covers 0.5 % of this area

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

Miocene nonmarine rocks (Oligocene to Pleistocene) at surface, covers 0.3 % of this area

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

Schist of various types and ages, unit 9 (Cargo Muchacho Mountains) (Jurassic(?)) at surface, covers 0.2 % of this area

Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.

pre-Cenozoic metasedimentary and metavolcanic rocks undivided (Early Proterozoic to Cretaceous) at surface, covers 0.2 % 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.

Tertiary volcanic flow rocks, unit 10 (Alverson) (Tertiary (14-18 Ma)) at surface, covers 0.1 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Tertiary pyroclastic and volcanic mudflow deposits, unit 6 (Jacumba) (Tertiary (12-19 Ma)) at surface, covers < 0.1 % of this area

Tertiary pyroclastic and volcanic mudflow deposits.

Undated granitic rocks, unit 3 (Southern California) (Jurassic(?) to Cretaceous(?)) at surface, covers < 0.1 % of this area

Undated granitic rocks unit 3

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.

Tertiary volcanic flow rocks, unit 11 (Jacumba) (Tertiary (12-19 Ma)) at surface, covers < 0.1 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Limestone of probable Paleozoic or Mesozoic age (Paleozoic to Mesozoic) at surface, covers < 0.1 % of this area

Limestone, dolomite, and marble whose age is uncertain but probably Paleozoic or Mesozoic

Oligocene nonmarine rocks (?), unit 2 (Southeastern California) (Cretaceous(?) to Oligocene(?)) at surface, covers < 0.1 % of this area

Recent (Holocene) volcanic flow units, unit 5 (Salton Sea) (Holocene) at surface, covers < 0.1 % of this area

Recent (Holocene) volcanic flow rocks; minor pyroclastic deposits; in part Pleistocene.

Lithology: rhyolite

Orocopia Schist (Late Cretaceous to Early Tertiary) at surface, covers < 0.1 % of this area

Mostly gray, fine-grained quartz-feldspar-mica schist, with sparse metabasalt and metachert. The unit is exposed in tectonic windows in the southwestern corner of Arizona. It is interpreted as metamorphosed marine sandstone that was tectonically emplaced beneath southwestern Arizona during early Tertiary subduction of Pacific Ocean sea floor. (65-165 Ma)

Jurassic volcanic rocks (Jurassic) at surface, covers < 0.1 % of this area

Massive quartz-feldspar porphyry, generally interpreted as thick, welded rhyolitic tuffs, with locally abundant lava, and sandstone and conglomerate derived from volcanic rocks. Rare eolian quartzite units are interbedded in southern Arizona. Includes Ali Molina Formation, Mount Wrightson Formation, part of the Canelo Hills Volcanics, Cobre Ridge tuff, Black Rock volcanics, Planet Volcanics, and equivalent rocks. (160-200 Ma)

Jurassic granitic rocks (Jurassic) at surface, covers < 0.1 % of this area

Granite to diorite, locally foliated and locally alkalic; includes Triassic(?) granitoids in the Trigo Mountains. This unit includes two dominant assemblages of igneous rocks. The Kitt Peak-Trigo Peaks superunit includes, from oldest to youngest: dark, foliated or gneissic diorite, medium-grained equigranular to porphyritic granodiorite, and small, irregular intrusions of light-colored, fine-grained granite. The Ko Vaya superunit, limited to south-central Arizona, includes texturally heterogeneous K-feldspar-rich granitic rocks. (150-180 Ma)

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

Con-glomerate, sandstone, mudstone, limestone, and rock-avalanche breccia (sheet-like deposits of crushed rock) deposited and tilted during widespread normal faulting and basin development. Sediments, mostly conglomerate and sandstone, are commonly medium to dark brown, reddish brown, or brownish gray; younger strata are generally lighter colors. Most deposits are 20 to 30 Ma in southeastern Arizona and 15 to 25 Ma in central and western Arizona. (11-32 Ma)

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

Lava, tuff, fine-grained intrusive rock, and diverse pyroclastic rocks. These compositionally variable volcanic rocks include basalt, andesite, dacite, and rhyolite. Thick felsic volcanic sequences form prominent cliffs and range fronts in the Black (Mohave County), Superstition, Kofa, Eagletail, Galiuro, and Chiricahua Mountains. This unit includes regionally extensive ash-flow tuffs, such as the Peach Springs tuff of northwestern Arizona and the Apache Leap tuff east of Phoenix. Most volcanic rocks are 20-30 Ma in southeastern Arizona and 15 to 25 Ma in central and western Arizona, but this unit includes some late Eocene rocks near the New Mexico border in east-central Arizona. (11-38 Ma)