AMARGOSA RANGE, IGNEOUS ROCKS. 
Valley and the Panamint Range and, like them, is considered in pari 
of Pliocene and in part of Pleistocene age. 
Probably representing stream gravels contemporaneous with 
older alluvium are small areas of conglomerate- dary ( Janyon 
and in the gulch in which Poison Spring is situa Boundary 
Canyon, near Hole in the Rock Spring, reddish 
upon the eroded surface of the Paleozoic rocks, from whicl 
ders have been derived. These bowlders reach a maximum diai 
ter of 3 feet. The stream bed of the Poison Spring gulch is largely 
cut in calcite-cemented conglomerates. At the mouth of the gulch 
these beds are 40 feet above the stream, but 2 miles above Poison 
Spring they are at stream level, indicating that the present grade is 
steeper than that of the stream which deposited these gravels. Calcite 
veins, many of which are banded, fill joint fissures in the conglomer- 
ates. In a few places narrow seams of limonite indicate that some 
pyrite was deposited with the calcite. 
IGNEOUS ROCKS. 
In addition to the hornblende gneiss and schist already described 
(p. 163), the igneous rocks of the Amargosa Range include post- 
Jurassic granite, pre-Tertiary diorite porphyry, and several Tertiary 
lavas. 
Granite porphyry. — Dikes of granite porphyry cut the Pogonip 
limestone miles northwest of the Staininger ranch. The rock has a 
grayish-pink fine-grained groundmass, which is exceeded in bulk by 
the phenocrysts. Unstriated pinkish-gray feldspars, which reach 
a maximum length of one-fourth inch, are more abundant than small 
rounded quartz phenocrysts. Rarely a little chlorite stained by iron 
suggests the former presence of biotite. Under the microscope the 
groundmass appears as a microgranitic aggregate of quartz, ortho- 
clase, and a little plagioclase. With the phenocrysts of orthoclase 
and quartz are some of biotite altered to chlorite and calcite and a 
few of plagioclase. This granite porphyry is probably one of the 
post-Jurassic granites. 
Diorite porphyry. — Fragments of a greenish-gray much-altered 
igneous rock occur in the desert gravels on the eastern slope of the 
range west of Rose's Well, and dikes of this rock probably cut the 
Cambrian sediments. The rock is apparently the pre-Tertiary dio- 
rite porphyry. 
Biotite an clesite— -The oldest of the Tertiary lavas is a biotite an- 
desite, which occurs in a number of small areas between Grapevine 
Canyon and Willow Spring, being particularly abundant near Mex 
can Camp. The biotite andesite is a dense lithoidal or semiglassy 
rock, which is gray, green, brick red, or purplish red. the last coloi 
evidently being due in many cases to alteration. Phenocrysl 
