SPRING MOUNTAINS
This is the eastern side of
the Spring Mountains, as seen from Cottonwood Valley, a little W-SW of Las
Vegas, southern Nevada, USA. Most of the rocks seen in this view are
Mesozoic in age. The reddish-colored, slope-forming unit at the base of
the mountains is the Chinle Formation (Triassic). The Chinle here is
overlain by a thick, light brown-colored, cliff-forming unit of
Navajo-equivalent quartzose sandstones (Jurassic). These two units are in
a lower thrust plate. A major thrust fault occurs at the top of the
brown, cliff-forming sandstone unit. Above the fault, in the upper thrust
plate, are dark-colored Paleozoic rocks. The upper thrust plate moved
eastward (from left to right in these pics) during the Sevier Orogeny
(Cretaceous).
