Submarine Geology of San Pedro Shelf

ABSTRACT The submarine area off San Pedro, California, consists of a shallow shelf which extends seaward 3 to 12 miles and is bordered by a steep escarpment leading down into the deep San Pedro Basin. The shelf and escarpment are cut by a prominent sea valley and two smaller valley-like features. Shale, limestone, and sandstone of middle Miocene age are exposed on the central shelf. Late Miocene mudstone crops out on the shallow inner shelf, and early Pliocene siltstone occurs on the steep escarpment at relatively great depths. The ages and distribution of the rocks indicate that the lithology and structure of nearby Palos Verdes Hills extends southeastward onto the submarine shelf and escarpment. Unconsolidated sediments on the shelf are subdivided into six types according to their texture and color. Finest sediment is found behind the breakwater inclosing the shoreward part of the area. Coarsest sediment is a yellowish brown sand on the central shelf and is believed to be residual from Pleistocene conditions. Sediment sorting within the area correlates well with known currents.