Vol. 6] Baler: Cenozoic History of the Mohave Desert. 



353 



and overthrust, as will be apparent from the accompanying 

 illustrations (pi. 39a and b). Locally the thin shales and inter- 

 bedded borax layers have been closely crumpled. Less com- 

 petent layers have crumpled under horizontal compressional 

 stresses where more competent beds have fractured or remained 

 undisturbed (pi. 40a). In this case it is clear that horizontal 

 movement along bedding planes has occurred. A later faulting 

 which has effected the strata of the Rosamond Series will be 

 considered elsewhere in this paper (p. 368). 



THE ROSAMOND SERIES IN THE TYPE LOCALITY AT ROSAMOND 



Strata, composed mainly of volcanic tuff-breccia, with inter- 

 calated flows of both acid and basic lavas, and a subordinate 

 amount of granitic breccia and bedded chert, rest on granitic 

 rock with a thin basal breccia along the track of the Southern 

 Pacific railroad about two and one-half miles north of Rosamond 

 station. In the vicinity of the railroad and eastward as far 

 as the west side of Rosamond dry lake the beds dip about 15° 

 to the southward. But at the western end of the exposure the 

 strike gradually changes from east-west to north-south and the 

 dip from south to west. Hershey's type section was given on 

 page 339. 



The thinness of the granitic basal breccia, which is wholly 

 absent in places, apparently indicates that locally at the time 

 of deposition of the basal beds the granitic land mass was of 

 rather low relief and even surface. The matrix of the basal 

 breccia is volcanic ash. Immediately next the granite in places 

 in the Rosamond locality, as well as locally in the Barstow syn- 

 cline and east of Red Rock Canon, is a pure white, fine-grained, 

 compact, porous rock which is probably a leached volcanic rock. 



Some four hundred feet above the base is an interbedded 

 now of red acidic lava exhibiting now structure and containing 

 obsidian, felsite, and dark gray perlite. Mammillary and botry- 

 oidal structures are very common in the interbedded lava. Be- 

 low this lava the tuff-breccia is locally cemented by an opaline 

 cement and in places contains seams and botryoidal masses of 

 chalcedony, incrusted by opal. The lava of the breccia is appar- 

 ently identical in composition, texture, and structure with that 



