Cortes and Tanner Banks are 90 nautical miles west of San Diego, California in a marine basin-range province, designated the "Continental Borderland." The two banks and the shah low saddle-like depression which separates them have all area of 230 square miles. Contours drawn at 10 fathom intervals reveal all extensive terrace at a depth of 40 to 60 fathoms on both banks. Sixty-six bottom samples obtained from the region permitted detailed studies of the rock and recent sediments. Only sedimentary and igneous rocks of Miocene age were found. The characteristics of the recent sediments are controlled by topography, current activity, and depth of water. An area of non-deposition or unconformity exists at the top of the banks.