7601

• UCREFRP Catalog Number: 7601
• Author: Minckley, W. L.
• Title: Native Fishes of Arid Lands
• USFW Year: 1991.
• USFW - Doc Type: A Dwindling Resource of the Desert Southwest.
• Copyright Material: NO

Figure 4. Left: Canyon-bound reaches alternating with more open sections in bends
characterize most desert rivers (San Juan River, photograph by U.S. Bureau of
Reclamation). Right: In wider, valley sections, meandering channels and sandbars are
common and riparian woodlands develop on floodplains (Gila River, New Mexico).

Figure 5. Left: Boulder Canyon reach of the Colorado River prior to Hoover Dam,
contrasted with; Right: the same reach after the dam was in place to form Lake
Mead, Arizona.Nevada (photographs provided by U.S. Bureau of Reclamation).

replaced from above, and unlined channels soon are
deeply incised. Arroyo cutting (Fig. 7) due to
watershed abuse such as overgrazing stimulates
further erosion, draining water tables to decrease
stability even more. Groundwater is pumped from
beneath the desert floor far faster than it is restored,
seepage into channels fails as water tables drop, and
streams cease to flow. Riparian vegetation disappears,

Figure 6. Imperial Dam, Arizona-California, a major diversion
on the lower Colorado River, from which canals supply
agricultural and domestic water for southern California
(photograph provided by U.S. Bureau of Reclamation).

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