WSPC06079

• File Number: 8064.100
• Description: Ute Tribes
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 6/1/1987
• Author: Boyle Engineering
• Title: Agricultural Engineering Study - Mancos Watershed - Task D-E - Final Report - Design-Cost Estimate for Off-Farm Irrigation Facilities and PIA Determination
• Water Supply Pro - Doc Type: Report/Study

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

14:.8

Bedrock formations in the study area are, in ascending order, the

Mancos Shale, the Point Lookout Sandstone, and the Menefee

Formation. The Menefee Formation consists of alternating sequences

of sandstone and carbonaceous shale with minor amounts of coal. It

is slightly friable but well cemented. The MeneEee is exposed in the

canyon walls. Geologic characteristics of this formation generally

make it sui table for dam and reservoir foundations. Locali zed

occurrences of coal and carbonaceous shales may require special

treatment during construction, but are unlikely to have a

significant effect on dam feasibility. The Point Lookout Sandstone

may be exposed locally at the base on the canyon walls. The Mancos

Shale probably underlies the entire study area but appears

everywhere to be overlain by the Point Lookout Sandstone and

therefore should not influence dam siting.

The depth of alluvium in the valley fill is estimated to average about

80 feet. It consists of clays, silts, and some gravels. Because of

the apparent depth and composition of the valley fill, it was

concluded that only zoned earth embankment or rockfill dams should be

considered. At this stage of the investigations, it is not felt the

depth and composition of the valley fill would be suitable for a

roller compacted concrete dam which would be desirable from the flood

capability standpoint.

Published mapping indicates some localized, small-scale landslides.
These would not, however, signi f icantly af feet dam si te feas ibili ty.

23