DESCRIPTIVE GEOLOGY. 
TOLICHA PEAK AND QUARTZ MOUNTAIN. 
TOPOGRAPHY AND GEOGRAPHY 
Tolicha Peak, a striking cone rising from Pahute Mesa, is a Land- 
mark for miles. Quartz Mountain, a somewhat lower east-wesl 
ridge, extends eastward from Tolicha Peak. The hills are bare, except 
for a sparse growth of desert shrubbery. Monte Cristo Springs, on 
the western slope, furnish sufficient water for 15 to 20 head of stock. 
GENERAL GEOLOGY. 
The formations of these mountains from the base up are Cam- 
brian (?) schist, post- Jurassic granite. Tertiary rhyolite, and Ter- 
tiary basalt. 
SEDIMENTARY ROCKS. 
Cambrian ( ?) schist. — The hill 2^ miles southeast of Tolicha Peak 
appears greenish gray in color at a distance, and is probably formed 
of a bluish-gray schistose rock which occurs abundantly in the deserl 
gravels to the south of this hill. The rock is very fine grained, except 
for some small crystals of biotite and hornblende. White, ellipsoidal 
areas 1 inch long spot the blue-gray rock. Under the microscope the 
groundmass appears as an exceedingly fine aggregate of quartz and 
feldspar, in which are embedded small areas of quartz, orthoclase, 
ragged hornblende, and biotite. The rock is probably a metamor- 
phosed Paleozoic shale, possibly of Cambrian age. 
IGNEOUS ROCKS. 
A specimen of rhyolite from Tolicha Peak collected by Mr. S. G. 
Benedict contains an inclusion of gray granite of medium grain. 
Post- Jurassic granite probably underlies this peak. 
Rhyolite forms Tolicha Peak and the east side of Quartz Moun- 
tain. The predominant type is a dense flinty rock of reddish color 
with a few small phenocrysts of glassy feldspar, quartz, and biotite. 
Flow lines, perlitic parting, and spherulites are well developed. 
Gray glassy facies, transparent in thin flakes, are interbedded with 
this type, as are white or light-gray incoherent facies in which the 
phenocrysts are abundant and equal the groundmass in bulk. Flow 
breccias are rather common. This rhyolite is probably about con- 
temporaneous with the earlier rhyolite of the Kawich Range and is 
presumably of early Miocene age. 
Prior to the extrusion of the basalt which covers Pahute Mesa 
(see p. 137) Tolicha Peak was eroded into a rugged mountain. The 
valley between Tolicha Peak and Obsidian Butte is upon the contact 
between the rhyolite and basalt. 
