250 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



change its trend through these latitudes it comes to lie, along southern 

 California, about one hundred and twenty miles farther out than it 

 did at Point Conception. 



Thus, within this wide, sweeping arc of the southern California 

 coast lies a great embayment of the sea. The continental shelf is wider 

 here than the entire width of the Coast Ranges of central California 

 and the submerged area is in general alignment with these ranges. This 

 section of the continental shelf thus represents a submerged part of 

 the continent; a mountainous section with peaks rising eight thousand 

 feet above the deeply submerged basins. Only the higher portions of 

 these mountains ranges rise above sea level, and form an archipelago of 

 scattered islands extending over an area of some five thousand square 

 miles. As this archipelago roughly parallels the coast, along which 

 coastwise vessels ply, the island group is called the Channel Islands 

 of California. These islands extend from 23.3 miles south of Point 

 Conception to 62.4 miles west of Point Loma. 



The Geologic Setting 



The area now occupied by the Channel Islands was in past ages the 

 scene of great epeirogenic activity. Reed (1933) states that this area 

 was a large island which he calls "Catalinia." This land mass, which 

 apparently existed from the Cretaceous to the early part of the Tremblor 

 formation of the Middle Micoene, extended west and south from the 

 present islands, probably including the Cortez and Tanner Banks, and 

 possibly also Guadalupe Island, two hundred and fifty miles to the 

 south of San Clemente Island. Intermittent periods of submergence 

 and uplift differentiate areas of this ancient land mass. Only occasionally 

 has it been connected with the mainland. Many plant endemics, many 

 of which are only distantly related to present mainland plants, and 

 some endemic animals are to be found on the islands. 



Figure 1 shows the relationship of the Channel Islands to each other 

 and to the southern California coast, as well as to the general contours 

 of the continental shelf. 



The northern four islands form the summits of a partly submerged 

 ridge extending westward from the Santa Monica Mountains. San 

 Miguel Island lies the farthest west, nearly due south of Point Con- 

 ception. The relative positions of the islands can best be visualized by 

 reference to Figure 1. During at least the latter part of the Cenozoic 

 the area about the four northern islands is thought by Reed (1936) to 

 have been a separate geological province, which he calls "Anacapia." 



