160 



Areas of Rock Bottom 



Rocks occurring in Santa Monica Bay are clzissified into 

 three groups? (1) bedrock, (2) gravel (transported rock), and 

 (3) phosphorite (a chemically precipitated rock). 



Bedrock 



The major area of bedrock exposed on the sea floor 

 occtirs on the outer shelf projection between the two sub- 

 marine canyons, and rocks that are believed to be in place 

 occur off Malibu and the Palos Verdes Hills, The major 

 rock types found on the outer shelf are shales, but mud- 

 stones, siltstones, and sandstones also occuro Some of the 

 rocks have been dated as Miocene in age. Fragments of schist 

 recovered from the outer shelf are either basement rock 

 (Jurassic or older) or from a Miocene-age breccia. Other 

 investigators have dredged rock from the Redondo or Santa 

 Monica Canyons. 



Gravel 



There are extensive patches of gravel in the nearshore 

 region, off Palos Verdes Hills, and near Malibu. Gravel in 

 extensive quantities is known to underly finer sediment in 

 other parts of the bay, but the full extent is unknown. Some 

 material of gravel size also occtirs in the fine sediment of 

 the bay, but is widely dispersed. The gravel fragments are 

 primarily composed of igneous rocks with lesser amounts of 

 metamorphic and sedimentary material. The major gravel 

 deposit far offshore is svurrounded by finer sediment, indi- 

 cating that it is relic and was not transported to this 



