Recent explorations on the Scripps Institution vessel have confirmed the impression obtained from previous work that there are extensive areas off the California Coast where deposition is either very slow or nonexistent. Dredging and coring operations show either rock bottom or a very thin sediment cover on most of the deep banks off southern California, on many steep submarine slopes, on the walls and even on the floors of submarine canyons, and on the outer portions of the continental shelves. Depth seems to have little bearing on these occurrences. Further possible evidence of absence of important deposition comes from the finding of sand and gravel in very deep portions of submarine canyons where mud should be the chief sediment. Sand was discovered even in portions of the troughs and basins off southern California at depths ranging around half a mile. This sand may be significant because the chief sediment being supplied to the deep areas at present, insofar as can be determined, is silt and clay. The importance of bottom currents and of submarine mud flows in preventing deposition is discussed.