138 



University of California. 



[Vol. i. 



a river meandering through a base-level plain in a region of very 

 "ancient" and "mature" topography. In this sense they are cer- 

 tainly very ancient compared with those of San Pedro Hill and San 

 Clemente, for the amount of degradation of the land is many hun- 

 dred fold that which has been effected in the case of these two 

 masses. (See Plate 8.) 



It tints appears that Santa Catalina was a land mass, subject to 

 the forces of snbaerial degradation, at the time when San Pedro Hill 

 and San Clemente began to emerge from beneath the zvaters of the 

 Pacific, in post-Pliocene time. 



Evidence of Subsidence. — Nor is this the end of our deduction. 

 An additional probability presents itself. The island seems to have 

 been subjected to a process of submergence which may even now 

 be active.* The emergence of land from beneath the waters of the 

 ocean is usually easy to detect, as has been exemplified in the case 

 of San Pedro Hill and San Clemente. The fact of submergence is 

 more difficult of recognition. Two chief characteristics of a sub- 

 siding coast are (i) the flooding of stream valleys and the conse- 

 quent formation of harbors, and (2) the more rapid recession of the 

 sea-cliffs than in the case of a stationary or rising coast. f Both of 

 these conditions seem to be fulfilled in the case of Santa Catalina 

 Island. The low pass which almost bisects the island at the "Isth- 

 mus," and the flooded portion of which forms the excellent shelter 

 known as Catalina Harbor, is almost beyond question a stream 

 gorge. The highest part of this pass is now less than 20 feet above 

 tide, and the hills rise abruptly on either side. As a stream gorge 

 it could not have been evolved at the present relative attitude of 

 land and sea. The gorge is almost completely submerged. The 

 conditions are, to say the least, strongly suggestive of a submer- 

 gence of the island. 



The argument from the sea-cliffs is not less forcible. Except 

 at one place near the south end of the island the sea-cliffs are not 

 remarkable for their height. They lack the continuity which marks 



*Dr. Cooper, in his visit to these islands in 1863, noted the absence of ter- 

 races on Santa Catalina, and surmised that it might be sinking. " Gaology of 

 California." Vol. I, p. 185. 



t See Gilbert, Lake Bonneville, U. S. G. S.. Monograph I, p. 73. 



