CHANNEL ISLAND REGION 



317 



dwarfing of the elephants before their final extinction, which occurred 

 earlier on San Miguel than on Santa Rosa. 



Fossil plants are known from terrace deposits on Santa Cruz Island, 

 and have been studied by Chaney and Mason (1934). They consist of 

 logs and fruiting structures, and represent nine species, three being 

 conifers and the rest dicotyledons. All are still living in California, the 

 modern forest most closely approximating the assemblage occurring at 

 Fort Bragg, 440 miles to the northwest. At the latter locality the tem- 

 perature is considerably lower and the rainfall greater than on Santa 

 Cruz Island today, indicating that similar conditions prevailed on the 

 island when the plants grew there. It is concluded by the above-men- 

 tioned writers that this was during one of the glacial ages of the Plei- 

 stocene. 



Still further evidence is given by the invertebrate fossils found on the 

 terraces of Palos Verdes Hills (Woodring, 1935). Fossil marine shells 

 occur on nine of the 13 main terraces, the highest being on the twelfth 

 terrace at 1,215 feet above sea level. These are generally tide-pool and 

 rock-cliff species, living today. However, the fossils from the lowest 

 (youngest) terrace were determined by Woodring (ibid.) to be of 

 Palos Verdes (late Pleistocene) age. This is confirmed by a recent Car- 

 bon 14 determination on one of the shells collected by Woodring, which 

 gives the age as "older than 30,000 years" (Kulp, et aL, 1952). The 

 indication is that the terraces were cut during the Pleistocene, and 

 probably during late Pleistocene, although it is conceivable that they 

 may be of more than one generation of terrace cutting. 



GEOLOGICAL HISTORY OF THE REGION 



It is seen from the foregoing that there are two widely divergent 

 sets of conditions to be met in attempting to work out the Pleistocene 

 history of the Channel Island region. If the submarine canyons were cut 

 by normal stream processes, the land must have risen or sea level have 

 been lowered by at least 1,000 feet and possibly as much as 2,000 to 

 3,000 feet. On the other hand, the terracing of Palos Verdes Hills and 

 San Clemente Island, and possibly of Santa Catalina Island, requires a 

 rise of sea level or a sinking of the sea floor and mainland by 1,325 to 

 1,500 feet. And following this there has been a return of sea level to its 

 present position. The net movement to be accounted for is a minimum of 

 approximately 2,500 feet and a maximum of 4,500 feet. 



It is possible, of course, as has been suggested, that part of the sub- 

 marine canyon cutting took place in the Pliocene, or perhaps even earlier 



