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

I
I
I
I
I

in an area known as Tepee Park, see Figure IV-8. This site appeared
to have a more efficient dam/reservoir while sacrificing the amount of
the basin water which it could control. These two Beaver Creek dam
sites were used for all further analysis.

2. Geologic and Geotechnical Analysis

I
I

The proposed Beaver Creek damsites are in the SE 1/4, Section
1, (Lower Beaver) at Township 7 South, Range 94 West, and at Tepee
Park in unsurveyed Section 26, Township 7 South, Range 94 West. No
previous geologic or geotechnical studies have been made of those pro-
posed damsites. A reconnaissance of the sites was made on July 25,
1985.

I
I

The geology of the Lower Beaver Creek damsites is typical of
that on the south side of the Piceance Creek Basin and north of
Battlement Mesa. The bedrock is the upper part of the Wasatch
Formation, which consists of lenticular sandstone, siltstone and
claystone beds. The beds are essentially horizontal or dip gently
(less than 50) to the west. At the Tepee Park site, the bedrock is
the Uinta and Green River Formations of the Tertiary Age. The Green
River Formation includes the Lower Green River and the Parachute Creek
members. The Uinta Formation overlies the Wasatch Formation and con-
sists of siltstone, sandstone, and marls tone. The Green River
Formation overlies the Uinta Formation and consists of siltstone and
marlstone. The beds are essentially horizontal. No major faults have
been mapped in the area (Ref. 33 ), but the sands tone units show
conspicuous jointing. The principle direction of jointing is parallel
to the bedding. Secondary joints are approximately at right angles to
the beds and parallel to the beds and parallel to the strike and right
angles to the strike.

I
I
I

I
I

I
I
I

The bedrock for the most part, is covered by surficial
deposits. The surficial deposits include colluvium, including
landslide deposits, and alluvial deposits, including terrace deposits.
The colluvium is derived by weathering of the underlying bedrock and
covers most of the slopes. The east side of Beaver Creek, below and
above the proposed lower damsite, and in the upper part of Tepee Park
have been mapped (Ref. 33) as an old landslide mass (see Figures IV-7
and IV-8). The landslide consists of boulders, cobbles and gravel of
basalt in a sandy and silty clay matrix. Small landslides, which are
the result of the saturation and failure of the colluvium, occur along
the west side of Beaver Creek. Alluvium occurs in the bottom of the
present stream valleys. Along Beaver Creek, it consists of boulders,
cobbles, and gravel of basalt in a sandy matrix. Older alluvial

I
I

IV-26