MOUNTAINS SOUTHEAST OF PAHUTE MESA. 
TIMBER MOUNTAIN. 
TOPOGRAPHY AND GEOGRAPHY. 
Timber Mountain, named on account of its heavily forested sum- 
mits, is bounded on the east and northeast by Fortymile Canyon, on 
the northwest and west by Oasis Valley, and on the south by Beatty 
Wash. A low divide connects it with Pahute Mesa to the north. 
massive mountain has two peaks, each 7,500 feet high, which arc sepa- 
rated by a col. The western slope to Oasis Valley is somewhat more 
gentle than that on the east to Fortymile Canyon. The heaviest 
forest growth in the area surveyed covers this mountain above an ele- 
vation of 0,300 feet. Some of the trees are of sufficient size to be 
of value as timber. 
GEOLOGY. 
* 
1 imber Mountain appears to be wholly composed of Tertiary rhyo- 
lite and basalt, the rhyolite being the older. 
Rhyolite. — The mountain peaks and the north and Avest slopes are 
formed of rhyolite, which imparts to the mountain a red tone. The 
most abundant variety is a dense brown or red rock in which the phe- 
nocrysts, medium-sized glassy orthoclase and slightly smoky quartz 
with fewer bronze biotite, equal or exceed the groundmass in bulk. 
The rhyolite is but an extension of that of Yucca Mountain, and the 
various facies there noted probably also exist on Timber Mountain. 
The rhyolite is presumably of early Miocene age. 
Basalt. — The rhyolite of Timber Mountain had been eroded into 
practically its present form when basalt was extruded, filling depres- 
sions in the rhyolite and forming level reaches here and there on the 
mountain. Basalt flanks Timber Mountain on the east, forms the 
prominent black dome 8 miles east of south of the more northerly of 
the two peaks, and occurs in several areas on the western slope of the 
range. The basalt is a dense black or dark-gray rock in which stri- 
ated feldspar and olivine phenocrysts are prominent. Much of the 
basalt is vesicular, and the rounded cavities, locally filled by zeolites, 
vary greatly in size across the flow banding. The basalt flow reaches 
a thickness of over 1,000 feet. The basalt of Timber Mountain is 
much younger than the rhyolite, and from the amount of erosion 
which it has suffered it is believed to be one of the late Pliocene or 
early Pleistocene basalts. 
BARE MOUNTAIN. 
TOPOGRAPHY AND GEOGRAPHY. 
Bare Mountain, so named on account of its almost total lack of 
verdure, lies south of Oasis Valley and Beatty Wash, between the 
Amargosa Desert and Crater Flat. The mountain mass is triangn 
in form, the apex being at the south end. It is 15} miles long from 
