1912] 



Baker: Western El Paso Range 



121 



tion along the strike of the basal beds of the Rosamond series of 

 sedimentary rocks. It thus separates the range in this vicinity 

 into two subsidiary ranges, the basalt-capped Black Mountain 

 on the north and the main granite ridge on the south. 



Sequence op Formations 



The rocks of the El Paso Range may conveniently be divided 

 into the basement complex of metamorphic and plutonic rocks, 

 the superjacent series of sedimentary and volcanic rocks, and 

 the alluvium. The basement complex comprises the rocks of the 

 higher divides and, with the exception of two minor localities, 

 of the whole southern flank. The sedimentaries and volcanics, 

 with the exceptions just noted, are confined to the northern flank. 

 The alluvium mantles in places all the older rocks. 



THE BASEMENT COMPLEX OP METAMORPHIC AND PLUTONIC ROCKS 



Metamorphic Quart zite-co)i glomerate and Quartz-schist in 

 Bed Bock Canon. — The lower narrows of Red Rock Canon have 

 been cut through a metamorphic series of quartzite-conglomerate, 

 quartzite, and quartz-schist of unknown age and thickness. This 

 series comprises the oldest rocks in the western portion of the 

 range. The quartzite-conglomerate is formed of well-rounded, 

 milky quartz pebbles averaging less than an inch in long diam- 

 eter, embedded in a matrix of impure quartzite with a noticeable 

 percentage of basic minerals which gives the rock a greenish-gray 

 to dark gray color. Under the microscope the quartz is seen to 

 form a holocrystalline fine granular mosaic with schistose struc- 

 ture. About ten per cent of the rock is made up of a green 

 hornblende, which is also recrystallized. Another slide shows 

 about as much epidote as quartz, with an irregular vein of calcite 

 including anhedral grains of a mixture of limonite and hematite. 

 The quartz includes acicular crystals, greenish-yellow in color, 

 which are probably epidote. Good slaty cleavage is developed 

 in portions of this series. Small masses of secondary pyrite are 

 to be seen in the quartzite. 



Intrusive Hornblende Dioritc-porphyrij. — The metamorphic 

 series is cut by a mass of hornblende diorite-porphyry. The 

 main intrusive rock has medium-sized and fairly abundant 



