134 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
rock at Trappmans Camp is a light-gray fine- to medium-grained 
biotite-muscovite granite. It forms low,. rounded hills and shallow 
valleys, and outcrops are inconspicuous. The granite is cut by several 
systems of intersecting joints and by faults and zones of brecciation. 
In consequence the residual masses are squared blocks, more or less 
rounded. Under the microscope the granite shows as an allotrio- 
morphic, granular rock, composed of orthoclase, quartz, plagioclase, 
biotite, muscovite, and zircon. The muscovite is in part original and 
in part an alteration product of feldspar. The rock has been consid- 
erably mashed, and quartz and muscovite have been deposited in the 
fractures of feldspar and quartz. 
The granite grades into and is cut by irregular masses and dikes of 
pegmatite, composed of feldspar and quartz anhedra up to 1 inch in 
diameter. Quartz stringers and veins of pegmatitic origin, some of 
which are several hundred feet long and 40 feet wide, are common. 
The quartz on portions of the borders of the larger masses contains 
fragments of granite and sends well-defined veins into the granite. 
At other place- single individuals of quartz on the contact seem com- 
mon to both pegmatitic quartz and granite, and arms of feldspar 
extend from the granite into the quartz. Evidently the quartz solidi- 
fied contemporaneously with some portions of the granite and subse- 
quently to other portions. A few thin dikes of fine-grained aplite, 
which stand in relief on Aveathering, cut the granite. 
A granite mass 1 mile long occurs in the midst of the Siebert lake 
beds 5 miles north of west of Whiterock Spring. It is low and cov- 
ered by a yellowish granite soil from which protrude low, rounded 
granite domes. Near its center is a rugged hill, set with sharp pin- 
nacles, whose forms are controlled by the well-developed joints. The 
granite is coarse grained and is composed of pink feldspar, Avhite 
semitransparent quartz, and biotite. Feldspar and quartz reach a 
maximum length of three-fourths of an inch. Under the microscope 
the granite shows as a hypidiomorphic granular rock formed pre- 
dominantly of large orthoclase plates poikilitically inclosing quartz 
anhedra and plagioclase laths. A little biotite is also present, and 
this, since it occurs along fractures in orthoclase, has been consider- 
ably recrystallized. The accessory minerals are titanite, apatite, and 
magnetite, the last probably titaniferous, since it is surrounded by 
secondary titanite. 
The granite is cut by narrow dikes of pink aplite, practically lack- 
ing biotite. These dikes weather in relief. In the granite are ellip- 
soidal masses of quartz-feldspar pegmatite from 4 inches to 5 feet in 
diameter, the contact between the granite and pegmatite being in 
some instances sharp, in others gradational. Feldspar and quartz 
individuals with a maximum diameter of 6 inches, together with a 
few biotite plates, compose the pegmatite. This rock grades into 
