PANAMTNT RANGE, IGNEOUS R< 
The basin is in Pogonip limestone and is probably the site of an 
ancient sink hole formed when the climate was less arid. Later 
channel became obstructed by the inwash of clebri mm the surron 
ing hills, and eventually alluvial slopes and a pla; were formed. 
RiM:iu's hocks. 
Earlier quartz-monzonite porphyry. — A few small fragii 
fine-grained, medium-gray igneous rock are included in the quartz 
monzonite in the southwest corner of the area mapped. Similar 
inclusions in the granite of Gold Mountain prove, on microscopic 
examination, to be quartz-monzonite porphyry. 
Quartz monzonite. — A batholith of quartz monzonite underlies 75 
square miles in the southwest corner of the area surveyed. The rock 
is light to. medium gray in color, rarely pinkish gray. The minerals 
visible to the unaided eye are predominant gray feldspar, a greenish- 
black mineral, either amphibole or pyroxene, bronze-brown biotite, 
and pink feldspar, while small individuals of magnetite and seal- 
brown titanite are also visible in places. As a whole biotite is almost 
as abundant as hornblende, but it appears to be totally In eking over 
restricted masses. The diameter of the component minerals varies 
throughout the mass from one-fourth to one thirty-second of an inch. 
In many places the gray feldspars occur as well-developed tablets up 
to three-fourths of an inch in length and impart to the rock a porphy- 
ritic aspect. Green epidote in granules replaces the hornblende and 
biotite more or less completely, while veins of epidote cut the rock, and 
felts of this mineral are common on joint surfaces. Calcite veins are 
less common. The monzonite is cut by joint planes from 1 foot to 5 
feet apart. In weathering the joint blocks become slightly rounded 
and finally disintegrate into soil. The monzonite forms rugged 
ridges. The outcrops are usually low bosses or bowlderlike masses, 
and many of the hills have the appearance of moraine-, upon which 
large bowlders are prominent. 
Under the microscope the rock shows an allotriomorphic granular 
texture, although some of the smaller plagioclase individuals form 
laths. The essential constituents, in order of abundance, are plagio- 
clase, orthoclase, piotite, quartz, hornblende, and ugite. The accessory 
minerals are apatite, magnetite, and titanite. Disks of micropegma 
tite lie between the other constituents and are inclosed in the feld- 
spars. Some hornblende is secondary to augite, while kaolin, sericite, 
and epidote form at the expense of the feldspars. The rock is on the 
border line between quartz monzonite and granodiorite. 
The monzonite is cut by thin dikes of a fine-grained pink aplih 
composed of feldspar and some hornblende. Quartz is someti 
seen in the rock, which then appears to be of granitic composition 
The dikes are usually simple. Under the microscope this rock \ 
