The Del Valle area is a part of an east-west synclinal basin located near the eastern end of the Ventura Basin. It is also a part of the Transverse Range region of southernCalifornia and its structural trends are therefore predominantly east-west. The area is characterized, structurally, by folding and overthrust faulting with some minor normal faulting. The formations consist entirely of sedimentary rocks ranging in age from Miocene to Recent. Beds of the Saugus, upper and lower Pico and Repetto formations are exposed at the surface, and consist of sands, sandstones, siltstones, and shales. Local terrace sands and gravels and alluvial deposits are also present. Two productive oil fields, the Del Valle and Ramona oil fields are located within this area.