40 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
the close of the Jurassic. This seems wvy probable from the genera] 
parallelism of the Nevada ranges with the Sierra Nevada crest line, 
particularly since some of the ranges west of the area surveyed are 
composed of folded Triassic and Jurassic rocks. At this time the 
Paleozoic rocks were complexly folded, the larger proportion of the 
flexures striking west of north. The folding in some places is close 
and in others open, being particularly intense in the ranges nearer the 
Sierra, such as the Panamint and Amargosa ranges. It was accom- 
panied by reverse faulting. These post-Jurassic structural lines have 
ever since their formation proved to be lines of weakness, of which 
advantage has been taken by later deformation. 
After considerable folding had taken place, and probably before 
{he end of the deformation, granitoid rocks were intruded into the 
Paleozoic strata. That the granite intrusion was a late event in the 
deformation i^ indicated by the massive character of that rock. The 
intrusion was accompanied by local buckling of strata, by contact 
metamorphism, and somewhat less directly by ore deposition. It 
was followed by the intrusion of a quartz -monzonite porphyry, and 
later of diorite porphyry and diorite. 
A long period of erosion, extending at leasl to Eocene time, fol- 
lowed the post-Jurassic folding and consequent mountain building. 
This period was probably one of heavy rainfall and large rivers. 
Xo estimate can be formed of the amount of erosion, but it was 
sufficient to remove from the granite the covering beneath which it 
solidified. Notwithstanding the length of this erosion period no 
peneplain was formed; from this it is inferred that the area was sub- 
jected to successive uplift- while being eroded. Where exposed be- 
neath the oldest Tertiary formation the Palezoic rocks appear to have 
been eroded into mountain ranges, many of which have a north! 
south extension. Some of these mountains of Paleozoic rocks — 
for example, the Kawich Range — were fully as high and rugged as 
the present range-. 
The Eocene inaugurated the Tertiary period of volcanism and lake 
sedimentation processes, accompanied by important deformation! 
erosion, and ore deposition. The Tertiary igneous rocks, being 
largely in flows, in contradistinction to the intrusive po-t -Jurassic 
rocks, produced but little contact metamorphism. The permanency of 
the structural lines, initiated probably in early Cretaceous time, has 
already been mentioned. Along these lines the Tertiary defor- 
mation occurred, while many of the main lava extrusions burst from 
north-south veins along pre-Tertiary mountain ridges. The firsj 
lava to outflow Avas a rhyolite, which was followed by monzonites and 
acidic andesites, in part intrusive bodies. Next there was an impor- 
tant and probably long erosional interval, followed by a mighty 
extrusion of rhyolite. which equals or exceeds in bulk the basalt out- 
