Quartz grain shape is a highly satisfactory natural tracer of sediment flux and accumulation. Sands from a river-beach-cliff complex near Oceanside, California were analyzed in terms of the variation of the closed-form Fourier amplitude spectra of maximum projection shapes of about 100 grains per sample. The data were analyzed by heirarchical analysis of contingency tables and discriminant functions. River, beach, and cliff samples were clearly defined. Results indicate that, at the end of the dry season, longshore drift had removed most of the sand of the San Luis Rey River from the beach, excepting an area adjacent to a pier where at least 25% of sand grains were river-derived. During the dry season the unconsolidated beach cliff is the dominant source of beach sand.