University of California. 



[Vol. 2. 



To the group with rugged topographic forms belong Santa 

 Catalina, Santa Cruz, and the larger part of Santa Rosa. Santa 

 Barbara and Anacapa Islands are of doubtful grouping, owing to 

 their small size. 



It is probable that all of the islands originated through 'crustal 

 deformation, for the most part as tilted blocks, though with the 

 information at present at hand, it can not be definitely asserted 

 for them all. San Clemente and San Nicolas are without doubt 

 faulted blocks; and Santa Catalina seems to be, in part at least, 

 due to faulting. San Miguel and Santa Rosa, with a minimum 

 depth of water of not more than 100 feet between them, would 

 appear to be a single faulted block, probably modified by differ- 

 ential movements within the mass. Whether the remaining islands 

 of this northern group, Santa Cruz and Anacapa, which apparently 

 form a single unit, originated at the same time and in the same way 

 as San Miguel and Santa Rosa, future field work alone can decide. 

 The remaining island, Santa Barbara, shows no block-like character. 



Description of the Islands with Simple Topography. — Of the 

 islands of the first group, San Clemente has been described by 

 Dr. Lawson* and the writer fas a tilted orographic block. It is 

 characterized by gentle slopes on the seaward side and abrupt 

 slopes on the landward side. The seaward slope is marked by an 

 unusually well defined series of terraces, up to an altitude of about 

 1,500 feet; — a series which (for reasons given later) is unequaled 

 elsewhere on the California coast. On the landward side only 

 fragmentary terracing occurs, where the slopes are locally com- 

 paratively gentle, as toward the northwestern end, where the rocks 

 are folded rather than faulted. Along the steeper parts of this 

 side not even traces of terraces are to be seen. 



The rocks of the island are for the most part hard volcanics, 

 only a small proportion consisting of less resistant sedimentary 

 deposits. 



The drainage of San Clemente Island is of post-Pliocene age, 



*The Post-Pliocene Diastrophism of the Coast of Southern California, Bull. 

 Dept. Geol., Univ. Calif., Vol. I, No. 4, 1893, p. 129. 



t A Sketch of the Geology of San Clemente Island, 18th Ann. Rept., U. S. 

 Geol. Surv., 1896-97, Pt. II, p. 467. 



