To obtain more detailed information concerning the nature of submarine canyons, diving operations were carried on in the heads of two typical canyons in the La Jolla area. Frank Haymaker, who dove under the writer's telephonic direction, described and photographed features which show that these canyons closely resemble the adjacent land canyons. Haymaker found vertical and even overhanging rock walls, narrow tributaries entering either at grade or as hanging valleys, and sediment-covered canyon floors. Cliffs of alluvium with layers of cobbles were discovered at the head of one of the canyons. In none of the 62 dives, extending over a period of a year, was there any evidence of significant density currents nor of the effect of any other strong currents moving down the canyon floors. The evidence suggests that the canyons were excavated by streams and that the heads are being filled but that the fill is removed from time to time by mud flows. Although the dives did not go deeper than 190 feet in the canyons, evidence is presented to show that the topography could not be due to moderate lowering of sea level.