Part of La Jolla Bay is occupied by five geographically distinct sediment types, based upon grain size. An isolated area now under forty fathoms of water contains coarse particles suggestive of a former beach on the rim of La Jolla Submarine Canyon; the other four types display a strikingly linear correlation of grain size with depth of water, represented by the following equation: Mud Percentage = 1.74 x (Depth in fathoms) -1.93. A sharp change in mud percentage is found at thirty fathoms, which may correlate with the seaward limit of eddy water movements near shore. The sands consist chiefly of subangular quartz and abundant feldspar. The widely different hydraulic properties of mica and dark minerals are shown by their correlation with depth. Organic remains are uniformly distributed. The apparent absence of a submarine canyon offshore from a prominent land valley suggests that the forces which clear and preserve two submarine canyons on the south are lacking farther north.