274 



University of California. 



[Vol. ir 



complex, but as yet it has been studied very little. In addition to 

 the Tertiary and Cretaceous there is a pre-Cretaceous uncrystalline 

 series and a basement complex of crystalline rocks. Many bodies 

 of eruptives of" various ages, and exhibiting a wide range in chemical 

 composition, are found in different portions of the area. 



One of the eruptive masses to be described lies in the extreme 

 southeastern part of the county, in the range of desert mountains 

 between the Carisa Plain and the Cuyamas Valley. The second 

 is found on the western slope of the Santa Lucia Range, about 

 seventy-five miles distant in a northwest direction. The third and 

 least important occurs on the Eagle Ranch, in the Santa Lucia 

 Range, about six miles west of the town of Santa Margarita. 



The range in which the 

 Cuyamas dike occurs is the 

 watershed between the San 

 Joaquin Valley and the Pa- 

 cific Ocean, having an ele- 

 vation of nearly 4,000 feet 

 in places. Topographically 

 it forms the connecting link 

 between two granite ranges, 

 the San Jose on the north- 

 west and the San Emedio 

 on the southeast. It rises 

 quite abruptly from the 

 broad and desert valley of 

 the Cuyamas, presenting a 

 most barren and forbidding 

 aspect. Owing to the absence of vegetation, the general geo- 

 logical structure is easily made out. Although no fossils have 

 been found 111 this range, yet the general nature of the forma- 

 tion and its relation to the known Chico-Tejon lying on the 

 northwest and west, indicate that it is of Miocene age. The 

 strata are but slightly consolidated, those of an argillaceous na- 

 ture predominating. The eruptive body, as far as is known, lies 

 wholly on the western side of the range. It begins nearly op- 

 posite the Spanish Ranch, about two miles from the valley, where 



Figure r. Index Map. 



