Prominent southern California streams were sampled at their mouths during a rainy season to determine the concentrations, grain sizes, mineralogy and quantities of suspended sediment supplied to the ocean by the southern California watershed. Approximately 3.5 million tons of suspended sediment are brought to the ocean annually by southern California streams. Some 0.8 million tons are arkosic sands, and the remaining 2.7 million tons of river-supplied sediment are silts, clays, colloids and dissolved material. The total annual supply of sand to the California coast has been previously estimated at 5 million tons. Approximately 4.2 million tons of sand can be attributed to stream traction load. It is concluded that southern California supplies 7.7 million tons Of terrigenous material to the Continental Borderland every year. This estimate agrees well with rates of supply which have been calculated from seismic profiling surveys.