80 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
that this basalt is to be correlated with that of Tonopah and the 
Monitor Hills and that it is of Pliocene age. 
Later rhyolite. — The eastern side of the hills on the boundary of 
the area is formed of rhyolite in flows. The groundmass, much of 
which is glassy, when fresh is white or light gray, but in places it 
is stained pink, yellow, or brown by iron oxides. Medium-sized feld- 
spar phenocrysts are more abundant than those of quartz and biotite. 
This rock is perhaps contemporaneous with the Oddie rhyolite" of 
Tonopah, which is younger than the Siebert lake beds. 
Later quartz latite. — The prominent isolated cone between the 
roads 4 miles west of north of Southern Klondike, several small ex- 
posures east of this cone, and a considerable portion of the northern 
pari of the hills east of the Tonopah-Goldfield road are composed of 
a lilac-gray igneous rock. A black glassy facies occurs on the east 
side of the cone. As phenocrysts, fresh and altered, feldspars are 
more abundant than quartz grains, biotite tablets, and hornblende 
columns. Under the micro-cope the groundmass appears as a spheni- 
litie glass in which considerable calcite is developed. Orthoclase 
predominates over plagioclase, which proved in one determination to 
be an acidic labradorite. Apatite, magnetite, and zircon occur as 
accessories. 
The latite is characterized by vertical flow lines, particularly near 
the contact with the rhyolite. and the mass is probably a volcanic 
neck. It is very similar to the Brougher dacite & of Tonopah, all 
though somewhat richer in hornblende, and the two are presumably 
contemporaneous and of Pliocene age. 
STRUCTURE. 
The Cambrian rocks have been complexly folded, the chief struc- 
tural feature being an anticline with a northeast -southwest axis. 
Superimposed upon this anticline are numerous lesser anticlines and 
synclines, and at many points the beds are intensely crenulated. The 
rocks are horizontal or dip at varying angles up to 1)0°, those of 45° 
predominating. The folding probably immediately preceded and 
accompanied the granite intrusion. Faults of small displacement 
occur, and brecciation is common. The sediments are cut in every 
direction by veins of calcite and less commonly by those of quartz. 
The veins are not folded, and hence fracturing occurred after the 
folding of the series and was probably connected with the granitic 
intrusions. Faulting and some tilting have occurred since the forma- 
tion of the Tertiary rocks, although it i< not known whether the tilting 
is dependent on faulting or is due to flexing without rupture. On the 
southern edge of the hills dikes of earlier rhyolite are faulted, hut 
a Spurr, J. E., Prof. Paper U. S. Geol. Survey No. 42, 1905, pp. 10-50. 
& lfeid,, pp. 44-48. 
