144 



Perhaps only a small number of schist fragments have been 

 found in the region because the original outcrop had been 

 covered by Miocene and later sedimentary deposits and only 

 recently was partially uncovered by erosion. Since Pliocene 

 age Forarainifera have been found both to the east and west of 

 the rock areas and only Foraminifera of the Miocene and Recent 

 periods in the rocky area, perhaps erosion in post-Miocene time 

 carried sediments from the topographically higher rocky area 

 leaving only Miocene and Recent age rocks where rock is now 

 exposed. If this is true, then the rock and gravel area has 

 suffered deep erosion, including deposits of the Miocene, the 

 Pliocene, and perhaps Quaternary periods. If deep denudation 

 took place in this part of the bay, the gravel might be a 

 residual deposit brought about by erosion and winnowing of 

 fine material. This process is similar to the accumulation 

 of "lag gravels" in desert regions in which the wind removes 

 fine-material and leaves a residual deposit of coarse gravel. 



In the El Segundo oil field, the Franciscan (?) or Catalina 

 schist is overlain by a schist conglomerate and nodular shale 

 at a depth of 7,000 feet below sea level. The conglomerate in 

 this oil field was formed by the weathering of the underlying 

 Catalina schist. It is conceivable, therefore, that the schist 

 fragments and the gravel on the outer shelf have a similar 

 origin, A possible argument against this theory is the almost 

 complete lack of schist fragments or gravel composed of schist 

 elsewhere in the region. In addition, the gravel is not 

 restricted to the rock and gravel region on the outer shelf, 

 but is found in scattered patches over the entire bay. 



