Turbidity-current sediment in the north end of San Diego Trough off southern California has produced a topography resembling that of a subaerial basin in the American southwest. Turbidity currents originating in submarine canyons cross subsea aprons that have accumulated at the foot of the mainland slope, and continue along channels in the trough floor until they spill over into the next basin. A channel and levee system aggraded 25 meters above the surrounding basin plain guides these currents for part of their journey in water 750 meters deep. This elevated system gives way to channels incised into the flat plain. Longitudinal profiles of the channels are smooth, continuous, and generally concave upward. The turbidites consist of gravel, sand, or coarse silt in beds that commonly display crossbedding, grading and shallow-water fossils. They are intercalated with hemipelagic green clayey silt whose rate of accumulation is about 11-21 cm/1,000 years. Sediment distribution is intimately related to the pattern of channels and other submarine topographic features. At least 100 meters of erosion by turbidity currents is indicated by deeply incised channels and terrace remnants on the lower part of Newport apron. Oceanside-Carlsbad apron, in contrast, is traversed only by aggraded channels having prominent levees. Turbidity currents were more frequent during Pleistocene time when sea level was lower and more submarine canyons headed near shore, to intercept coarse sediment moving along shore.