24 



U. So Coast and Geodetic Survey soundings were used almost 

 exclusively in that area. 



Submarine Physiographic Provinces 



The general physiographic divisions of Santa Monica Bay 

 ares (1) the Shelf, (2) Redondo and Santa Monica submarine 

 canyons, (3) the Basin Slope, and (4) Santa Monica Basin. 



Shelf 



For convenience in describing the submarine topography 

 and other portions of this report, that part of the shelf 

 that lies between the two submarine canyons is designated the 

 "outer shelf", or "central shelf projection". The Santa 

 Monica Shelf extends to a depth of approximately 270 feet. 

 At this depth a pronounced steepening of the sea floor 

 indicates the shelf break. The width varies from a few 

 hundred feet at the head of Redondo Canyon to more than 8 

 miles between the two submarine canyons. North of Santa 

 Monica Canyon the shelf is very constant in width ajid the 

 edge follows the shape of the present coastline. From Figures 

 5, 6a, & 6b, it can be seen that the bottom slopes seaward 

 evenly and has a gradient of about ^ degree. 



Nearshore, where sandy beaches are present, one or more 

 parallel troughs and ridges are often present. These long- 

 shore troughs and bars are generally transitory, moving up 

 and down in the nearshore zone and their presence, absence, 

 and position depend upon currents, storms, the tide, and wave 

 height. The shifting of sand, and even gravel along the bottom 



