WSP07583

• File Number: 8270.200
• Description: Selenium
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 1/1/1996
• Author: USGS
• Title: Detailed Study of Selenium and Other Constituents in Water-Bottom Sediment-Soil-Alfalfa and Biota Associated with Irrigation Drainage - Uncompahgre Project Area and in the Grand Valley - 1991-93
• Water Supply Pro - Doc Type: Report/Study

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Figure 2. Selecled features in the Uncompahgre Project area.

Geologic Setting

Rocks exposed in the study area range in
age from Precambrian 10 Upper Cretaceous. The
Mancos Shale. the terrace deposits on the western
side of the Uncompahgre Project. the valley-fill
deposits in the eastern cnd of the Grand Valley
(the cobble aquifer), and the alluvium overlying the
Mancos Shale are the primary geologic units affected
by irrigation in the slUdy area. Olher rocks in the

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study area primarily are exposed on [he outer edges
of the irrigated valleys. The following descriptions
of the geology of the study area were derived from
Meeks (1950), Williams (196-t), Lohman (1965).
Craig (1971), Schneider (1975). Th'ela and others
(1976), Schwochow (1978). Cashion (1973). Bureau
of Reclamation (1986a). and Sleven and Hail (1989).
Geologic maps of the irrigated parts of the study area
are shown in figures 4 and 5.

INTRODUCTION 7