HOOVER DAM
(aka Boulder Dam)
Hoover Dam (Boulder Dam) is
on the Nevada-Arizona border, east-southeast of Las Vegas. It dams the
Colorado River in Black Canyon & the water ponded up behind it forms Lake
Mead. The dam itself is impressively big at 726 feet tall. Built
over 6 years in the 1930s, the dam was intended to serve as a flood-control
structure, to create a water supply, and to generate electricity.
The rocks on either side of
Black Canyon at Hoover Dam include volcanics, siliciclastic sedimentary rocks,
and intrusive igneous rocks. The light-brown rocks dominating the photo
below are part of the Hoover Dam Tuff (inf.), consisting of volcanic tuffs
(welded ash-flow tuffs) of early Middle Miocene age (~14 million years).
The dark brown layer in the lower right corner of the photo is a latite sill,
intruded after deposition of the tuff beds. Note that the sill is offset
by a subvertical fault. There's a whole series of very obvious faults
lining the canyon walls downstream from Hoover Dam.
Above: view of southeastern side
of Black Canyon from atop Hoover Dam. Looking SE.