147 



It would appear, therefore, that on the basis of available 

 data there is a considerable thickness of sediment between the 

 coast which probably becomes thinner towards the outer shelf 

 as shown in Figure 38„ Although sedimentary rocks of various 

 ages may be covered by only a thin veneer of Recent sediments 

 in the inner shelf region, it is highly improbably that basement 

 occurs at or near the surface anywhere in this area. A detailed 

 study of fathograms taken over most of the shelf indicated that 

 most of the inner shelf out to a depth of about 170 to 180 feet 

 is a depositional plain. This suggests that deposition of sedi- 

 ments has covered a large portion of rock of Pleistocene age 

 and older which possibly at one time were exposed at the surface, 

 However, some areas, such as the regions where red sand occurs, 

 and at the head of Santa Monica Canyon, relic sediments have not 

 been covered. Since some of these relic sediments do not have 

 any discernable relief, they must be at equilibrium with the 

 present depositional surface, and as sediments are spread evenly 

 over the entire region they will be covered. This assumes, of 

 course, that most of the shelf is undergoing aggradation, and 

 there appears reason to believe that this may be partly true. 



No definite statements can be made for most of the other 

 parts of the bay since data are lacking. Nothing is known 

 concerning the age of the rocks beyond the shelf break, but a 

 large variety of rocks have been dredged from the submarine 

 canyons by Emery and Shepard (1945). A few of the rocks had a 

 possible age of Pliocene, but it appears as if the bulk of the 

 rocks should be dated as Miocene. No schist has been found in 

 the canyons. This imposes a very interesting questions If the 



