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<br />o <br />N <br />o <br />o <br />c <br />o <br /> <br />~--., <br /> <br />minerals from the soil and shale and carries them in solution to the <br />Colorado River as return flows in drains and as direct flows through <br />ground water aquifers. <br /> <br />An inadequate cross-drainage system has resulted in problems in <br />operation of the Government Highline Canal. An insufficient number of <br />cross-drainage structures was originally provided to convey natural run- <br />off from above the canal to drains flowing to the Colorado River. Only <br />six cross-drainage structures are found along the canal in the Stage One <br />area. Five of these are at least partially plugged with sediment and <br />debris, and none drain into chamlels adequate to carry .predicted 2s-year <br />floodflows. <br /> <br />5. Geology and Soils <br /> <br />The Grand Valley has been eroded by the Colorado River from Mancos <br />Shale, a formation of marine origin which underlies all of the land in <br />the Stage One area and much of the land in the valley. The shale contains <br />a high percentage of salts, and gypsum is commonly found in open joints <br />and fractures. The formation is impervious at depth but a weathered zone <br />near the surface transmits water along joints, fractures, and bedding <br />planes. <br /> <br />Nearly all of the soils in the Stage One area are medium-fine to <br />fine-textured soils derived from the Mancos Shale although some localized <br />gravel deposits occur in the western portion of the area. Soil depths <br />vary from a few inches to over 50 feet with the deeper soils the most <br />productive. The salt content of the soils generally increases with depth. <br /> <br />6. Vegetation <br /> <br />Vegetation in the Stage One area consists of the irrigated crops and <br />areas of native vegetation. The native vegetation is mostly limited to <br />narrow bands of greasewood, cottonwood, tamarisk, and associated species. <br />Saltbush is predominant on the desert lands north of the Stage One area <br />and on some small hills below the canal. The table on Page C-I shows the <br />approximate areas of vegetative types in the Stage One area. <br /> <br />7 . Fish and Wildlife <br /> <br />There are no established fisheries in the Stage One area. Highline <br />Lake, just west of the area on Mack Wash, receives its water supply from <br />the Government Highline Canal. The lake is a state-operated recreation <br />and fishing site. <br /> <br />The majority of fish species found in the Colorado River in the Grand <br />Valley have been introduced. Two of the native species, the Colorado <br />squawfish and the humpback chub, are Federally classified as endangered <br /> <br />B-3 <br />