NO. 3 dunkle: plant ecology, channel islands 251 



The presence of fossil elephants on Santa Rosa and Santa Cruz (Stock, 

 1935) indicates that there must have been a land connection with the 

 mainland in the early or middle Pleistocene. This evidence is further 

 substantiated by the presence of many plants with northern affinities 

 on the northern islands. This invasion of northern plants is thought to 

 have occurred during the glacial stages of the Pleistocene (Leconte, 

 1893). 



The four southern islands are much more widely scattered and 

 form the high points of submerged northwest and southeast ridges. 

 Santa Catalina, the largest of the southern islands, lies only twenty-two 

 miles south of Point Vicente. The second in size, San Clemente, the 

 most southern of the islands, is sixty-three miles west of La Jolla, while 

 the third largest of the southern islands, San Nicolas, lies farthest from 

 the coast, sixty miles from the nearest point of the mainland. Santa 

 Barbara is the smallest of the islands and is situated about half way 

 between San Nicolas and Santa Catalina. 



A fact of some interest in considering the location of the islands 

 is that the channels separating them from the mainland are shown by 

 Coast and Geodetic Survey charts to be about twice the depth of the 

 channels separating England from France, Asia from Alaska, and 

 Borneo, Java, and Sumatra from the Malay Peninsula, these latter all 

 being less than 100 fathoms in depth. The Catalina Channel is ap- 

 proximately the same depth as the arms of the north Atlantic separating 

 Iceland both from Greenland and from Europe. This not only shows 

 the deep subsidence of this portion of the continental shelf, but indicates 

 that there has been little possibility of any connection of the islands with 

 the mainland during the lower ocean levels of the Wisconsin glacial 

 stage of the ice age, unless diastropic agencies have considerably altered 

 the levels existing at that time. 



Figure 2 shows the islands in such a manner that their sizes may 

 easily be compared, and also shows the fifty-fathom contour which 

 roughly marks the lower limit of the beaches existing during the Wis- 

 consin stage. 



Past Climatic Changes 



Another element in the geologic evolution of the islands is the long 

 term change which has occurred since the early Pliocene, interrupted 

 by the glacial stages of the Quaternary and by long term cycles since. 

 The overall change has been a gradual drying of the climate. In recent 

 time the general record of geochronological climatology has shown a 



