Area 9 of Region 2 (Pacific Coast) encompasses the Sierra Nevada, western Great Basin, and Mojave Desert geomorphic provinces. Hydrocarbons are unknown as seeps or shows in wells. As a future oil province, this area appears to be of low order of importance because of intensive tectonism, plutonic activity, and varied degrees of metamorphism imposed on the Paleozoic section; a paucity of Mesozoic strata; and the limited areas of marine Tertiary rocks. Hydrocarbon entrapment is possible in the Great Basin and in the limited areas of possibly marine Tertiary rocks adjacent to the San Andreas fault and along the Colorado River.

Post-Cambrian, pre-Mississippian sequences, where present, are mainly carbonate rocks deposited in a miogeosynclinal environment. As a result of the Antler orogeny, which occurred largely in Nevada from latest Devonian to Early Pennsylvanian time, Mississippian and Pennsylvanian rocks adjacent to this orogenic belt are made up of coarse clastic material, as they are also in the Inyo Mountains. However, carbonate rocks are predominant eastward. Post-Cambrian to Permian rocks have reservoir characteristics in the Great Basin province.

The Sonoma orogeny of Late Permian and Early Triassic time resulted in the deposition of coarse clastic materials which could serve as reservoir beds in the Great Basin province. The Nevadan orogeny, associated with the Sierra Nevada and Mojave Desert plutonic events, and the Sevier orogeny on the east during Late Jurassic and Early Cretaceous time, resulted in removal of rock material from most of this area, particularly the Mojave Desert. Jurassic beds are clastic with good reservoir character but are limited to the easternmost part of the area. Cretaceous strata, if deposited, subsequently were removed.

These orogenies and the Laramide orogeny in latest Cretaceous and early Tertiary time involved much of the area in extensive thrust faulting and associated faulting and folding, and, during Tertiary time, Basin-Range block-faulting was superimposed on this structural complex.

Tertiary deposition was terrestrial, and volcanic activity was widespread. Sedimentary rocks of middle to late Tertiary age are confined to long narrow basins and contain much terrestrial clay, sand, and gravel; thicknesses of units are varied.