142 



Structure 



Figure 37 is a generalized diagram showing the lithology 

 of the upper few hundred feet of sediments near the shore. The 

 impervious clay cap in the upper part of the San Pedro formation 

 is believed by ground water geologists to extend only to the 

 shore in the region shown by the diagram. However, a similar 

 clay cap was found at the site of the Santa Monica breakwater 

 and also along the old Hyperion outfall course. In the 

 latter case, however, the clay in the cores may or may not be 

 the same clay cap identified on land, but at the Santa Monica 

 breakwater the clay cap was found in every core, at or very 

 close to the surface of the sea floor. The "Silverado zone" 

 of the San Pedro formation probably extends only 2 to 3 miles 

 offshore, but the other formations lower in the geologic 

 section may extend far out onto the shelf. 

 4 Two geologic formations in the Los Angeles region may be 



correlative with the schist cropping out on the shelf; the 

 Catalina schist and the San Onofre breccia. The San Onofre 

 breccia is Middle Miocene in age; the Catalina schist may be 

 pre-Cambrian or Mesozoic (Jurrasic ?). The Catalina schist 

 underlies almost all of the Los Angeles region and crops out 

 in the Palos Verdes Hills, The San Onofre breccia was formed 

 by the erosion of the underlying Catalina schist, and consists 

 of angular blocks up to 10 feet in diameter (Woodford, e_t al . , 

 1954, p. 71). Even though there is a significant difference 

 in the age between the Catalina schist and the San Onofre 

 breccia, it is difficult to assign a definite age to the 

 schist fragments found in Santa Monica Bay. 



