128 



University of California. 



[Vol. i. 



by Pliocene formations, this epoch of erosion must have been the 

 same as that which is generally recognizxd in California geology as 

 the post-Miocene uplift. There thus appears to have been an 

 important interval of denudation between the Miocene uplift and the 

 depression which permitted the deposition on the lower flanks of 

 the hill of the formations which paleontologists recognize as of 

 Pliocene age.* The recovery from this Pliocene depression is the 

 uplift which is registered in the elevated strands of the hill. The 

 Pliocene strata were probably deposited at an early stage of the 

 depression, and were slightly deformed by movements which affected 

 the coast, or by local causes, and were subsequently truncated and 

 terraced when again brought within range of wave action by the 

 uplift at its later stages. The Pleistocene strata which overlie the 

 Pliocene doubtless also belong to a recent stage of the uplift. It 

 follows that, while there is a very profound physical break between 

 the Miocene and Pliocene, the marine Pliocene and Pleistocene 

 formations are intimately associated, with no epoch of subaerial 

 denudation between them. 



SAN CLEMENTE ISLAND. 



Physiography. — If we disregard the Los Coronados group of 

 rocks, which lie off the Mexican coast, San Clemente is the most 

 southerly of the Channel Islands of Southern California. It is sit- 

 uated at a distance of about fifty-seven miles from the mainland. 

 Its southern extremity is but little north of east of San Diego, and 

 is due south of San Pedro Hill. The island is long in proportion 

 to its width, and its longer axis has a northwest and southeast 

 trend, being parallel to the opposite shore of the mainland. Its 

 length is twenty-one miles. The southeast third of the island has a 

 breadth of four miles, while the remaining two-thirds tapers towards 

 its northwestern extremity, where it is only a mile across. 



The topographic features of the island are simple, yet of an 

 exceedingly severe cast. Bare of timber and supporting besides 

 grass only a scant shrubbery and various varieties of cacti, the relief 



* Dall's statement of the Neocene (probably Pliocene) age of the middle 

 stratum of Deadman's Island, taken in connection with the writer's strati- 

 graphical observations, is the warrant for the identification of the Pliocene at 

 San Pedro Harbor. Cf. Bull. 84, U. S. G. S., p. 216 and map, PI. II. 



