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A geologic-mapping project sponsored jointly by the U.S. Geological Survey and the California Geological Survey San Bernardino 30' x 60' quadrangle (Morton and Miller, 2003), which adjoins the Los Angeles sheet on the east. The modified nomenclature results in some local generalizations of the map. In addition, the Quaternary surficial deposits have been relabeled according to standardized SCAMP nomenclature where data permit. The bedrock units of the area are commonly described in two principal groups: 1) Basement rocks-early Cretaceous and older, crystalline metamorphic and igneous rocks; and 2) The superjacent sequence of late Cretaceous and Tertiary strata. The greatest contrast in basement character is at the boundaries of the San Gabriel Mountains-Soledad Basin block. The San Gabriel Mountains form a basement massif that includes components of Proterozoic, Paleozoic, and pre-middle-Cretaceous Mesozoic metamorphic and plutonic rocks. These are the oldest basement rocks in the Los Angeles quadrangle and appear to represent old continental crust at the western margin of the North American craton, and which has been thrust over Jurassic oceanic crust of a different metamorphic facies than is found in adjacent blocks. In the eastern Los Angeles Basin, to the south of the San Gabriel Mountains, and in the Santa Monica Mountains, to the west of the San Gabriel Mountains, the basement rocks are metasedimentary and metavolcanic rocks of Jurassic age, that were probably deposited on a Jurassic oceanic crust, and accreted to the margin of the North American craton; they have been intruded by early Cretaceous granitic bodies of the same age as similar rocks in the San Gabriel Mountains, but the closeness of their relationship is not clear. The basement rocks of the western Los Angeles Basin also are associated with a Jurassic oceanic crust; however, their metamorphic character is significantly different, including blueschist facies schists that represent metamorphism in a subduction zone. The basement in the Topatopa Mountains block is unknown, but in the Santa Ynez Mountains, a few miles to the west, the basement is Franciscan Formation, including schists very much like those of the western Los Angeles Basin basement rocks. The superjacent sequence consists of Upper Cretaceous and Tertiary sedimentary and volcanic strata that rest unconformably on the crystalline basement. The regional unconformity at the base of the Upper Cretaceous is expressed only in the central Santa Monica Mountains, where the Trabuco Formation overlies basement rocks. Another regional unconformity, at the base of the Paleogene section, can be seen in the western Santa Monica Mountains and the Simi Hills where the Simi Conglomerate overlies the Upper Cretaceous sequence. The middle Miocene disruption of the pre-middle Miocene sequence and the formation of more localized basins is expressed by more restricted unconformities at the bases of latemiddle Miocene and younger strata and extreme variations in thickness of late Miocene and younger units....