WSP05382

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications-Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1975
• Title: The Natural Salinity of the Colorado River
• Water Supply Pro - Doc Type: Publication

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~ Plateaus. These plateaus are carved from a thick succession of strata of
~ mostly sandstones and shales, deeply dissected by the river and its
~ tributaries (Fig. 3). The surrounding highlands, exporters of water, are
Q the primary source of the river but the water's quality downstream is
largely determined by its travel across the plateaus. If the thick
sandstones in the succession are the makers of great canyons, cliffs, and
bridges (Fig. 4), the shales are the spoilers of the water quality. Add a
few faults across the stream that bring deeply circulating saline water to
the river and salt domes (Fig. 5) that lie in the path of some tributaries,
and the major natural villians are named in the degradation of the high-
quality water from the highlands as it loses its quality in passing toward
the sea.

The shales of the Colorado Plateaus were deposited mostly in
shallow seas that were often restricted and very saline and deposited
much calcium sulphate, if not sodium chloride, and even potassium
salts. The oldest shales that have a significant affect on the quality of the
Colorado are those of the Pennsylvanian Paradox Formation. Deposited
in a restricted sea centered near the Four Corners area, and adjacent to a
rapidly rising Uncompahgre Highland to the northeast, the black shales
grade into anhydrite and sodium chloride. These easily deformed lenses
of shale and salt, pressured by the weight of overlying Permian

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Figure 3, The Grand Canyon from the south rim, ArIzona.

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