The Marine Geology of the San Nicolas Island Region, California

San Nicolas Island is an anticline, modified by folding, faulting and marine terrace cutting. Terracing is believed to have taken place during the Pleistocene. Total submergence of the island is considered probable. Wave erosion along the present coastline has developed a series of sandy pocket beaches separated by rocky promontories. East flowing longshore currents, particularly along the northern coast, have deposited a large, pointed sand spit at the southeastern end of the island. The shape of the spit was found to have changed considerably during historic time. The shelf north of the island is broad and flat and is mostly rocky, being covered locally with patches of shelly sand and gravel. This northern shelf is very similar in character to the shelf north of Santa Catalina Island, although the San Nicolas shelf is larger. The shelf south of San Nicolas is narrow and sloping and is covered for the most part by terrigenous sand and sandy mud. Eocene Foraminifera have been recovered from a number of submarine outcrops near the island. Several outcrops on the outer edge of the northern shelf have yielded siliceous casts of what may be Miocene Foraminifera. Recent Foraminifera from the shelf sediments have been investigated and show depth zonation in general agreement with that established by Natland (1933) and more recently by Butcher (1951)