126 
SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
bands of red. purple, gray, and brown, the name of the range h 
derived. Of the many rhyolitic facies perhaps the most commor 
lias a rather dense reddish groundmass, in which are embedded 
medium-sized phenocrysts which equal or exceed it in bulk. The de 
script ion of the phenocrysts of the earlier rhyolite of the Kawicl 
Range applies almost equally well to those of this formation. Biotite 
however, is the predominant phenocryst in a facies outcropping 1. 
miles northwest of Cliff Spring. Hornblende phenocrysts arc ven 
rare. The rhyolite varies in color from white gray, brown, or pur 
pie to black. In texture the groundmass varies from glassy witj 
well-developed flow lines, perlitic cracks, and spherulites througl 
pumiceous to lithoidal. The rhyolites in the vicinity of Wheelbarrow 
Peak are more glassy and appear to be poorer in phenocrysts, particu 
larly quartz. Chalcedony is abundant on joint planes, and throughou 
the area surveyed an unusually great development of this form o 
secondary quartz i^ associated with the more glassy facies. The onjj 
thin section examined proved to be a normal rhyolite with partiall; 
devitrilied brown glassy groundmass. 
E 
Desert gravels 
Desert gravels ^_^L-^ ; ,T7~^:Il',<\' IT 1 ^''; 1 -;!^^: ,, , "_ Jk^^jl- 
Fig. 12. Easl wesl section .-icmss Belted Range through Belted Peak. 
Near (lill Spring the red rhyolite of the dill's has been bleacher 
to a yellowish white by surface waters along joints and irregula '! 
cracks. The contact between the bleached and unbleached portions 
is unusually sharp. The joints are often offset regularly, and th ! 
bleaching follows such offsets. Microscopic examination shows tha 
the bleaching is due to the removal of the hematite coloring matte 
of the somewhat devitrifiecl glass. It is probable, in consequence 
that considerable portions of the white chalky rhyolite of the rang 
have been produced by similar bleaching. 
Columnar jointing, due to contraction during cooling of the lavj. 
is particularly well developed on a hill isolated in the wash. \\ mild 
west of Cliff Spring, to the north of the road. The columns are fron 
6 to 12 inches in diameter and vary in position from vertical tj 
horizontal, intermediate directions being common. 
The rhyolite as seen on either flank of the range is clearly a f1o\ 
which in place- is over 2,000 feet thick. Belted Peak has some of tl ' 
characteristics of a vent (fig. 12), although the rhyolite may have bee i| 
extruded from a long fissure near and parallel to the crest line, a su< | 
gestion which, however, requires for proof more careful field observe - 
