PROJ00259

• Contract/PO #: C153424
• Contractor Name: Colorado River Water Conservation District
• Water District: 0
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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potential use for new irrigation ,mter generated by the West Divide
Project.

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Two storage sites were id,mtified in the Mamm Creek basin,
both are located on West Mamm Creek (See Figure IV~6). The upper site
is more efficient in terms of storage but it does not control a large
drainage area. The lower site has the capability of storing water
from Middle Mamm Creek via a short diversion canal. Both sites were
selected for further study.

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2. Geologic and Geotechnical Analysis

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Two possible damsites werE! identified on West Mamm Creek.
The lower site is on West Mamm Creek near the corner common to Section
7, 8, 17, and 18, Township 7 South, Range 92 West. The upper site is
on West Mamm Creek in the SW 1/4, Section 13, Township 7 South, Range
92 West and the adjacent portion of Section 24. No detailed geologic
or geotechnical studies have been made of these proposed dam sites.
A geologic reconnaissance of the sites was made on July 25, 1985.

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The geology is typical of that along the south margin of
Piceance Creek Basin. The bedrock is the lower and middle member of
the Wasatch Formation of Tertiary Age. The lower member, the Atwell
Gulch member, consists of lenticular sandstone, locally conglomeratic
sandstone, siltsone and claystone. The middle member, the Moline
member, consists of sUtsone and claystone wi th lenses of sands tone.
The beds are on the west flank of the West Divide Creek anticline, the
axis of which is about 1 to 2 miles to the east. The beds dip 1. to
5. northwest. No major faults have been identified in the area, but
the sandstone units are well jointed. The principal joints are
parallel to the bedding. Secondary joints are approximately at right
angles to the bedding and parallel to the strike or at right angles to
the strike.

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The bedrock is concealed for the most part by surficial
deposits. The surficial deposits include colluvium, which includes
landslides and rockfall deposits, and alluvium, which includes terrace
deposits. Colluvium is derived by the weathering of bedrock and accu-
mulates on the slopes and at the base of slopes. It consists of angu-
lar blocks and gravel of sandstone in a sandy and sUty clay matrix.
Where thick deposits of colluvium have developed and become saturated,
by precipitation or snowmelt, slope failure has occurred and landslide
deposi ts have formed. Small landslide deposits were not noted in East
and West Mamm Creeks. At the base of steep slopes below sandstone
cliffs, blocks of sandstone have accumulated to form small rockfall,
or talus, deposits.

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IV-22

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