PROJ00414

• Contract/PO #: C153326
• Contractor Name: Fruitland Mesa Water Conservancy District
• Contract Type: Grant
• Water District: 0
• County: Montrose
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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Available literature indicates that numerous low angle thrust and

normal faults, anclinical and synclinical structures are present

within a distance of five to fifty miles from the Gould Reservoir.

The trends of the faults range from north-south, northeast-southwest,

and northwest-southeast. These faults cut through Cretaceous sedimen-

tary rocks, Tertiary igneous rock, and pre-Cambrian igneous rocks.

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Gould Reservoir is located in Seismic Zone 1 as defined'in "Recour-
mended Guidelines for Safety Inspection of Dams" prepared by the Corps
of Engineers. An earthquake of the magnitude that would be expected
in Seismic Zone 1 should not cause significant distress to a well-
designed and constructed earth dam. Available literature indicates
that 22 historic earthquakes occurred near Montrose with a maximum
epicentra1 intensity of VI at a distance of 18 miles southwest of the
dam site. No Quaternary faults exist in the regional area of the dam
site.

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For design purposes it is recommended that a peak horizontal
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ground acceleration of 0.05g be used and the stabiiity of the embank-
ments be checked for O.lg.

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Site Geology

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The dam site is located at the upper end of Iron Creek Canyon on
the southeastern edge of Fruitland Mesa. Upstream and downstream of
the dam site the geologic regime is essentially flat-lying, inter-
bedded sandstones and shales. The high topography of Fruitland Mesa
is capped by the flat-lying Cretaceous Dakota sandstone, while at the
dam site the beds suddenly dip moderately to the southeast. In the
reservoir area there is no high topography, only flat-lying beds
exist, as can be seen along Colorado 92 just east of the reservoir.
The site geology represents a monoclinal fold probably related to the
uplifting of Fruitland Mesa. The low, flat area comprising the
reservoir basin is composed of Cretaceous Mancos shales that overlie
the Dakota sandstone. The topography to the east of the reservoir is
also flat-lying shales until the more rugged volcanics are encountered
a few miles away. The site Geology is presented in Figure 5.

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