150 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
ECONOMIC GEOLOGY. 
Although the Cambrian rocks are cut b}^ thin veins of white crys- 
talline or banded calcite and by thin quartz veins, apparently barren, 
they appear to offer slight attractions to the prospector. The John- 
nie mine, where strong quartz veins occur, lies 2 miles south of the 
area surveyed. From information furnished by prospectors it is 
probably in the Prospect Mountain quartzite. 
YUCCA MOUNTAIN. 
TOPOGRAPHY AND GEOGRAPHY. 
Yucca Mountain is so called from the groves of the tree yucca 
which cover its lower slopes. The group lies between Fortymile Can- 
yon on the east, Beatty Wash on the north, Oasis Valley and Crater 
Flat on the west, and the Amargosa Desert on the south. The 
mountains of the main east-west ridge are gently sloping domes with 
rugged summits, the highest of which is C>,700 feet above sea level. 
The ridge drops rather suddenly to Fortymile Canyon on the east, but 
on the Avest it descends gently and merges with Bare Mountain. 
From the main east -west ridge mesa tongues extend southward to 
the Amargosa Desert, rhyolite being the predominant rock. Yucca 
Mountain is colored dull tones of gray, brown, red, and yellow. Near 
the summits the varying resistances to erosion of the rhyolite flow beds 
are expressed in cliffs and gentle slopes. Spires tend to form where 
vertical joints are well developed. The mesa tongues to the south 
become lower toward the south-southeast, the surface being deter- 
mined by resistant lava flows. The eastern side of these mesa 
tongues passes beneath the Recent alluvial deposits, while the western 
face is, as a rule, a scarp. The magenta-red basaltic cone 4 miles east 
of Rose's Well is a prominent landmark. Other volcanic cones are 
located in Crater Flat and for convenience will be described with 
Yucca Mountain. 
The wide and open character of Beatty Wash between Timber and 
Yucca mountains is noteworthy. Alluvial deposits cover the depres- 
sion for a width of 2 miles, although many hills of solid rock protrude 
from them. The narrowness of the canyon farther downstream is due 
partly to the more resistant character of the rhyolite to the west, 
while the width of the upper valley is probably due to the rapid 
waste of the adjoining high mountain masses on either side. 
No water is known in Yucca Mountain. A few junipers and 
pinons grow on the highest summits of the main ridge. 
GENERAL GEOLOGY. 
This mountain is composed entirely of igneous rocks, which include 
(he following, beginning with the oldest: Post- Jurassic pegmatite. 
rhyolite and latite, and basalt. 
