It has been shown that sediments are being introduced into the ocean along the Southern California coast largely by swollen streams during the winter floods. There are, however, extensive areas of the sea floor off the coast on which no appreciable sedimentation is occurring. There is reason to believe that by-passing is the general rule on continental and insular shelves, on banks, ridges, steep submarine slopes, and in submarine canyons. Also deposition is thought to be very slow on the broad saddles between banks and islands and other deep topographic highs. Evidence has been presented to show that much of the coarse debris introduced by streams is returned to the land as beaches and later in part is blown farther landward by onshore winds. On the other hand finer sedi ents, principally silts and clays, are believed to be accumulating along the gentler slopes and in the basins and troughs.

The areas that are preserving a state of marine unconformity are characterized by abundance of rocky outcrops and by the markedly uneven texture of the sediments both laterally and vertically. Much of the coarser detrital material in these areas appears to be derived from an older generation of erosion and deposition probably related to former low stands of sea-level. Far from shore, however, other materials of sand texture, notably recent and fossil foraminifera, miscellaneous calcareous fragments, and glauconite predominate because of the removal by currents of the finer clastic sediments that would otherwise accumulate in these environments. Evidence is given to show that the by-passing on steep slopes and in the submarine canyons is in part the result of mud flows or other sliding action.

The sediments of the basins and troughs are predominantly clays of uniform texture and compare in fineness of grain with the sediments of the deep ocean and with those of protected estuaries along various coasts. The exceptionally high organic matter content of the basin sediments is one of their striking characteristics and is thought to be due to the virtual stagnation of the water below sill depths. The presence of fine-grained calcium carbonate below the surface in core samples from the basins may also be ascribed to the alkaline reducing conditions accompanying low oxygen supply.