320 CLEMENTS 



in the Tertiary. However, the great thickness of marine Pliocene known 

 to exist in the Los Angeles and Ventura basins, and the fact that rocks 

 containing marine Pliocene fossils have been dredged up offshore indicate 

 that the region was submergent rather than emergent in the Pliocene. It 

 does not seem logical that canyons cut earlier than Pliocene would remain 

 open during an epoch of submergence and deposition. 



It is the present writer's opinion that the first great lowering of sea 

 level (perhaps accompanied by actual uplift of the land) that initiated 

 the cutting of the submarine canyons came in early Pleistocene time, con- 

 currently with and as the result of the accumulation of glacial ice on the 

 continents in the Nebraskan glacial age. The effective lowering of sea 

 level amounted to approximately 3,000 feet, and converted the Channel 

 Island region into a great archipelago with long southeasterly-extending 

 peninsulas and fringes of islands 150 miles of? the present shore (see 

 Plate I). Between the peninsulas, gulfs or bays occupied the present deep 

 basins, and some of the shallower basins such as Santa Monica and the 

 one between Palos Verdes Hills and Santa Catalina Island were alto- 

 gether landlocked and probably contained lakes. 



The greatly increased gradients of all streams and the greater rainfall 

 as the climatic belts were forced to the south by the advancing ice sheets 

 increased the cutting power of the streams immensely. Existing channels 

 were extended across the newly exposed land surface, and were rapidly 

 deepened, and new channels that never reached back as far as the present 

 shoreline were developed. 



It was at this time, in all probability, that the elephants, moving south 

 before the advancing cold, wandered onto the peninsula formed by the 

 present northern group of islands, as well as occupying the Los Angeles 

 area. And it was probably at this time, too, that the more northerly forest 

 flourished on this same peninsula. 



Whether or not a similar emergence, of the same or smaller magnitude, 

 occurred during the Kansan and Illinoian glacial ages, the record does not 

 indicate. An inundation of the region occurred, however, at some time 

 later than the above-mentioned emergence. This must have been in part 

 from the return of water to the sea from the melting of the glaciers, but 

 actual rise of sea level was accompanied or followed shortly by a lowering 

 of the coastal area by perhaps as much as 1,500 feet. 



This brought about the reduction of the northern peninsula to a 

 chain of islands smaller than at present, with the drowning of parts of 

 the Ventura and the Los Angeles coastal plain areas. Likewise, Palos 

 Verdes Hills and San Clemente were reduced to small islands, and San 



