The Southern Lowlands consist of Miocene and Pliocene sands, clays, and gravels. These overlie oil and natural gas deposits, especially north of the Los Bajos Fault. The Southern Range forms the third anticlinal uplift. The rocks consist of sandstones, shales, siltstones and clays formed in the Miocene and uplifted in the Pleistocene. Oil sands and mud volcanoes are especially common in this area.