98 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
ation to a blood-red serpentine. Vesicular facies of the basalt are 
usually reddish brown and scoriaceous facies are brick red. In some 
beds angular fragments of basalt are embedded in a matrix of similar 
basalt, forming a How breccia and showing that motion continued in 
the lava after some portions had solidified. The more dense facies 
show spheroidal weathering well developed. Vesicular basalt bounds 
a central sheet of dense basalt and a ropy surface. The original flow 
surface is seen at place-: this indicates that the larger portion'of the 
basalt is without doubt a flow. The largest mass, however, is prob- 
ably the site of the vein from which the flows occurred. 
Where the contact between the basalt and the Siebert lake beds is 
exposed the basalt is seen to lie upon the eroded surface of the sand- 
stone. While it is possible that some masses of basalt on the lower 
hill slope- are Hows contemporaneous with the Siebert lake beds or 
are later sheets, they are more probably portions of the flow which 
owe their position partly to the uneven surface of the tuffs and 
partly to later deformation. The basalt, on structural and lithologij 
grounds, is believed to be contemporaneous with that of Tonopah, 
which Spnrr" believes to be of late Miocene or early Pliocene age. 
STRUCTURE. 
The Siebert lake beds and the basalt flows are in a broad way hori- 
zontal, although they have been tilted slightly to the northeast. The 
relative distribution of the basalt and the lake beds i^ such as to sug- 
gest that they are cut into a number of blocks by intersecting systems 
of normal faults. 
CACTUS FLAT. 
Cactus Flat lies between the Cactus and Kawich ranges. Its 
center i> occupied by a series of playas with north-south trend, 
which during very exceptional rains merge into one another. They 
are from .'>.:;:;<) to 5,350 feet above sea level, and are surrounded by 
low sand dune-. In this valley the Recent detrital deposits may be 
thick. The valley from the Cactus to the Kawich Range across 
Cactus and Gold flats illustrates the steeper slope of valleys near 
large and high mountain masses and the gentler grade near small 
and low hills. 
GOLD FLAT. 
Gold Flat lies between Pahute Mesa and the Cactus and Kawich 
ranges. Its lowest point. 5,035 feet above sea level, is occupied by 
a playa, 4 miles west of which, in a -mall inclosed basin, is another 
playa. North of the larger playa. at an elevation of 20 to 100 feet 
above its surface, are a number of round intensely dissected hillocks. 
"Spurr, .1. ]■:., Prof. Paper r. s. Geol. Survey No. 12, L905, p. <;«.». 
