10 
The floor of Santa Monica Bay is composed of six bottom 
material types: rock, gravel, sand, silty sand, sandy silt, and 
silt. The extent of rock outcrops was determined with a rock 
dredge which in many lowerings broke off fragments of rock, 
Pieces of siliceous and non siliceous shale were most frequently 
recovered, but one large fragment of schist representing a 
portion of a breccia was also recovered. Bathymetric data 
indicate that the rock outcrops rise as irregular and scattered 
mounds. The gravel surrounding the outcrops consists chiefly of 
coarse sand, well-rounded granules, and pebbles of granite, shale, 
chert, quartzite, schist, and gneiss. The gravel is relic 
material formed at a lower stand of sea level during the Pleis- 
tocene epoch. 
The overall pattern of the bottom material consists of a 
normal decrease of particle size away from the coast, modified 
by the areas of relic gravel and rock and fine grained material 
in a nearshore portion of Redondo Canyon. Silt-sized grains are 
most abundant in deep water areas of the bay where wave and 
current action are slight. 
The bottom sediments are generally olive-gray color; however, 
this may vary according to the amount of organic material present. 
The offshore sand, composed largely of shell fragments, is light 
olive-gray and is probably being deposited at the present time. 
Nearshore is detrital sand brought to the bay by streams from 
the north during the winter and spring. This sand has a more 
yellow or reddish color than that found offshore. 
The average median diameter of the sediments in Santa Monica 
Bay is 0.116 mm and the range is from 0.005 to 1.05 mm. A plot 
