152 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
4 miles east of Rose's Well. The basalt of the cones is vesicular and 
dull brick-red or black in color, while in the flow pediment around 
the cones are dense black facies with a few greenish glassy grains 
of olivine. 
The cones are gently depressed and are usually superimposed 
upon circular basalt flows. The flows present ropy surfaces, cross 
fractures produced during the flow of the almost solid mass, and 
caverns formed by the onflow of the liquid interior after the surface 
had hardened into a crust, each a characteristic phenomenon of sur- 
face lavas which have been but little eroded. The cones themselves 
are formed in part of flows, but largely of vesicular lapilli, scoria 3 , 
and volcanic bombs. The intimate mixture of these red and black 
fragments imparts to the cones their magenta-red color. The cone 
4 miles east of Rose's Well has on its summit a crater, 300 feet in 
diameter, which is depressed from 15 to 75 feet below it-^ rim. Sul- 
phur coats the volcanic breccia in the crater. The crater of the cone 
7 miles north of Rose's Well has been largely destroyed by erosion, 
the throat displaying a rubble of vesicular basalt fragments. Beds 
of fragmental material dip inward toward a common center at the 
crater of the cone U miles farther north. 
Since the eruption of the basalt the cones have been somewhat 
eroded, calcium carbonate has been deposited in the vesicles, shrub- 
bery has taken root on the lava flows, and a sand dune has been super- 
imposed upon the cone 4 miles* east of Rose's Well. The basalt is 
probably of very late Pliocene or early Pleistocene age. 
STRUCTURE. 
The rhyolite-latite series has been subjected to mountain-building 
forces acting in an east-west direction. Joint sheeting and normal 
faults striking north and south are developed in the mas-, while minor 
joints of east-west strike are also present. The series had been carved 
into forms approximating those of the present day when basalt erup- 
tions occurred. 
ECONOMIC GEOLOGY. 
Two small masses of rhyolite whose location is shown on the ma]) 
(fig. 4, p. 43) are kaolinized and silicified in a similar manner to the 
rhyolite in the vicinity of ore deposits. Silicification has occurred 
along joints and in irregular forms, and these resistant masses form 
the topographic details peculiar to silicified areas of rhyolite. Tunnels 
have been driven in the larger of the two areas, the ore extracted be- 
ing a silicified rhyolite slightly stained by limonite. The ore. in part 
free milling and in part refractory, is said to carry gold with minor 
silver values. Quartz does not seem abundant in either area. 
