194 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
field hills. The rhyolite immediately above the sandstone is in many 
places vesicular and is a flow breccia. 
This rhyolite is similar lithologically to the later rhyolite of the 
Goldfield hills, and the two have suffered equal deformation. They 
are without much doubt contemporaneous lava flows of Pliocene age. 
Basalt. — Black vesicular basalt occurs in a number of small outlier^ 
upon the Cambrian rocks, the granite, and the earlier rhyolite and as 
small buttes on the border of Slate Ridge. The basalt is similar 
lithologically to that of Mount Jackson and, like it, is probably of 
Pliocene or early Pleistocene age. 
STRUCTURE. 
The Cambrian rocks at a distance from granitic intrusions lie in 
gentle folds many of whose axe- trend northeast. The folding is 
comparable in intensity with that at Cuprite and Lida. On the other 
hand, they dip steeply away from the granite batholith and in its 
vicinity are buckled and minor isoclinal folds are common. (See fig. 
16, p. lsT.) It is evident that in this region the Cambrian rocks were 
folded prior to the intrusion of the granite, a process which superim- 
posed upon tin gentle fold- complex elements. The 1 granite is cut 
by normal faults. Since the Tertiary rocks were formed the ridge 
has suffered domical uplift, centering 1 or 5 miles east of the State- 
line Mill. 
ECONOMIC GEOLOGY. 
Quartz vein-, some of which are of pegmatitic origin, cut granite 
and the more metamorphosed Cambrian rocks. The best prospecting 
ground is the granite and the metamorphosed limestone and -hales in 
it- vicinity. In the late sixties mines were opened on Slate Ridge and 
considerable ore bodies were removed. The ledge at the Stateline 
Mill, now abandoned, is said to have been 20 feet wide, the ore averag- 
ing s|n per ton in gold. Recently a number of claims have been 
located in Slate Ridge and development work is now being done. 
The Bullfrog-George prospect i- situated on the side of a domical 
granite hill, near the Lida-Old Camp road. The surrounding hills 
are cut by quartz veins which weather in relief and can be traced for 
long distances. Some of these contain feldspar and others grade into 
pegmatite dikes. The Bullfrog-George claims an 1 situated on a 
quartz vein from 4 to 9 feet wide, which is traceable for about a quar- 
ter of a mile. The vein is vertical and strikes N. 70° W. The con- 
tact with the granite is in some places gradational, the white trans- 
lucent quartz of the granite passing into that of the vein without 
break. In other places the granite appears to have been shattered 
prior to the deposition of the quartz, which now fills linked cavities 
in the granite. The feldspars of the granite within 4 feet of the vein 
are locally much kaolinized. Apparently isolated in the quartz are 
