1912] 



Baker: Western El Paso Range 



123 



THE SUPERJACENT SERIES OP SEDIMENTARY AND VOLCANIC ROCKS 



In a previous paper by the writer the extensive bedded de- 

 posits of tuffs, tuff -breccias, and lava flows on the northern flank 

 of the El Paso Range were grouped with the Rosamond series 

 on the basis of lithologic similarity and similar fossil content to 

 strata farther south in the Mohave Desert originally given that 

 name by Hershey. 4 



West of Red Rock Canon the metamorphics are overlain un- 

 conformably by a lava flow called by Gilbert an "orange, massive, 

 subspherulitic rhyolite." The writer made no examination of 

 this rock. 



East of Red Rock Canon the quartzite-conglomerate, quartz- 

 ite, and hornblende diorite-porphyry are overlain unconformably 

 by a loosely-cemented breccia containing angular fragments of 

 the underlying rock. The matrix is mainly silicious sand rang- 

 ing in size up to coarse grit and fine pebbles. 



Farther east, where the Rosamond unconformably overlies 

 the granite, there is at the contact a pure white, silicious, compact 

 rock about twenty feet thick, overlain by several hundred feet 

 of red breccia, with thin interstratified beds of light gray tuff- 

 breccia, grading up into light gray tuff-breccia. 



On the east wall of Last Chance Gulch the basal Rosamond 

 lies unconformably upon the granite. The basal beds are coarse 

 water-worn conglomerate with a matrix of dark red granite 

 arkose and bowlders and pebbles mainly of granite, some bowlders 

 being as large as a foot in diameter. The immediate over- 

 lying beds are coarse and of varied hue, sometimes with inter- 

 bedded red and grayish-white layers, sometimes with cream- 

 colored or yellow or pink or dark red layers. A short distance 

 above the base the rounded conglomerate passes into angular 

 breccia. 



The basal sediments in Red Rock Canon consist of two hun- 

 dred and fifty feet 5 of dark red breccia, with thinner inter- 

 stratified layers of light gray color. Next in the upward succes- 



* Some Tertiary formations of southern California, Am. Geol., vol. 29, 

 pp. 349-372, 1902. 



5 All thicknesses given in the following descriptions are only approximate 

 estimates. 



