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University oj California. 



[Vol. 2. 



are carved, are small and comparatively shallow, for the most part 

 merely notching the surface just above the shore line. These 

 surfaces, further, have a gentle slope favorable to rapid cliff reces- 

 sion. On the steeper slopes of San Nicolas and San Clemente 

 Islands the stream courses are short and of unusually high grade, 

 and the slight development of their valleys gives conditions still 

 more unfavorable to flooding. Anacapa and Santa Barbara Islands 

 are similar to the islands with simple topography, as regards stream 

 development. Their small size precludes any large streams, and 

 the conditions are therefore unfavorable to valley flooding. 



The conditions most favorable to valley flooding, among the 

 islands, are found among those with rugged topography. Many 

 of their valleys, as compared with those of the islands in general, 

 are broad and deep, with moderate grade near their mouths. The 

 rocks of these islands being comparatively resistant and their sea 

 cliffs comparatively high, the conditions are also favorable to the 

 continuance of the drowned valleys, especially where the exposure 

 to wave action is least. All of these islands show drowned valleys, 

 those of Santa Catalina being the largest and most pronounced, 

 while those of Santa Rosa, as might be expected from the char- 

 acter of its topography, are the least evident. 



Thus the evidence from valley flooding is positive on the more 

 rugged islands, and favorable to a comparatively recent depression. 

 Since the evidence on the other islands is merely negative, it can 

 not be stated that they have not suffered recent depression. Judg- 

 ing, then, from the positive evidence of their submarine features, — 

 identical in character with those about the more rugged islands, — 

 it seems that the recent depression has been general for this part of 

 the coast. 



Historical Sketch. — It is generally assumed that the broad 

 physical features of the Pacific Coast were largely developed during 

 the prolonged period of erosion between the Miocene and Pliocene, 

 and that these forms have been modified more or less by subse- 

 quent movements, both general and local, as well as by subsequent 

 erosion and deposition. During the Miocene the land was depressed, 

 as indicated by the Miocene deposits, the nonconformity between 

 these and the Pliocene deposits showing a period of subaerial 



