SANTA ROSA ISLAND. 



By Eev. Stephen Bowers.* 



The approximate geographical position of the central portion of this 

 islai)d is latitude 33° 55" north and longitude 120° 8^' west. The 

 island is fifteen miles long by ten miles in width, the general shape being 

 that of a parallelogram, and contains about 75,000 acres. Its longer 

 axis is parallel with the line of the coast and the Santa Inez Mount- 

 ains, which form the northern side of Santa Barbara Channel. The 

 channel between Santa Eosh Island and the island of Santa Cruz has a 

 width of five miles, and that between Santa Eosa and San Miguel a 

 width of four miles. The depth of water around Santa Eosa Island is 

 less than that of the other islands. The outline of the island is bold, 

 and no harbor exists aroui.d its shores. There are, however, several 

 places where vessels can laud, and the i^resent jiroprietors, the Messrs. 

 Moore Brothers, have built a wharf on the eastern end of the island, 

 where vessels can load and unload at any time, except when gales pre- 

 vail from the northeast. 



Geology. — This island has been described as being composed of sand- 

 stone, but the first thing we observed upon landing was that the eastern 

 end of the island is composed principally of volcanic rocks. At the 

 wharf we found a good exposure of strata, forming cliffs about 30 feet in 

 height, the lower portion, for about 15 feet above the sand of the beach, 

 composed of stratified sandstone, fine grained, and destitute of fossils, 

 with an occasional stratum of breccia or conglomerate. These strata 

 have a dip of from 12° to 14° southeast. The upper portion of the cliffs 

 consists of a horizontal deposit of fragments of rhyolite, trachyte, vesic- 

 ular basalt, and white bituminous slate. The fragments gradually 

 decrease in size from the bottom upward, and are cemented together 

 with volcanic sand. The whole is covered with a deep and apparently 

 good soil. In some iilaces the rock fragments in the upper half of the 

 cliffs have been water worn and form conglomerate. This character of 

 rock extends from the wharf southeasterly to near a sand-point at the 

 southeastern extremity of the island, where it culminates in a hill of 

 volcanic rock 175 feet high. This is exposed for some distance in a 

 southerly direction from the beach on the north side of the point. The 

 rocks have a tendency to weather into odd and fantastic forms, the 

 angular ones becoming rounded by disintegration, irregular cavities 

 and caves being worn in it by the winds. 



*Dr. Lorenzo G. Yates, of Centreville, Cal., rendered me valuable assistance in the 

 exploration of this island. The geology is principally compiled from his notes. 

 31C 



