7983

• UCREFRP Catalog Number: 7983
• Author: U.S. Department of the Interior.
• Title: Quality of Water, Colorado River Basin.
• USFW Year: 1993.
• USFW - Doc Type: Progress Report No. 16,
• Copyright Material: NO

GEOLOGY AND SOILS 7

natural channel for about 10 miles below Davis
Dam at which point the river enters the broad
Mohave Valley 33 miles above the upper end of
Lake Havasu.

Lake Havasu backs up behind Parker Dam for
about 45 miles and serves as a forebay from
which the Metropolitan Water District of
Southern California pumps water into the
Colorado River Aqueduct. Lake Havasu also
serves as fore bay for the Central Arizona
Project, Havasu pumping plant, and pumps
water into the Hayden Rhodes Aqueduct. Alamo
Dam and Reservoir, on the Bill Williams River,
is used to control floods originating above and
below Alamo Dam.

Headgate Rock Dam, Palo Verde Diversion Dam,
and Imperial Dam all serve as diversion
structures with very little storage. Imperial
Dam, located some 150 miles downstream from
Parker Dam, is the major diversion structure to
irrigation projects in the Imperial Valley and
Yuma areas. It diverts water on the west bank
to the All American Canal, which delivers water
to the Yuma Project in Arizona and California
and Imperial and Coachella Valleys in
California. It diverts on the east bank to the
Gila Gravity Main Canal.

The Senator Wash Dam, an off stream storage
facility, also affords regulation in the vicinity of
Imperial Dam and assists in the delivery of
water to Mexico. This facility is used for
pumpback storage and recreation.

The Morelos Dam, located just below the
Northern International Boundary with Mexico,
is the last dam on the Colorado River. This
small diversion dam diverts water into the
Alamo Canal which delivers water to northern
Mexico.

GEOLOGY AND SOILS

The geology of the Colorado River Basin is
highly varied. Igneous, metamorphic, and
sedimentary rock types are present and range in
age from approximately 625 million years old to
recent alluvial deposits. Structural features,
including anticlines, domes, and faults,
contribute to both the topographic relief and the
geohydrology of the region.

Several of the sedimentary formations in the
Basin were deposited in marine or brackish
water environments. Occurrences of bedded and
disseminated sodium chloride (halite) and
calcium sulfate (gypsum) are observed, as are
clays with high contents of exchangeable sodium
and magnesium.

The soils of the Colorado River Basin closely
resemble the geologic formations from which
they were derived. Residual soils derived from
shale or sandstone are generally shallow. These
soils can contain appreciable soluble mineral
content due to residual and secondary mineral
formation from the parent material. Upon
weathering or irrigation, salts may accumulate
on or near the surface due to evaporation or
consumptive use by plants.