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bird-food items were collected at wetland sites. Bird eggs were collected and incubated. Bioassay samples were collected in March 1992 from five of the major streanls in the Grand Valley and analyzed by the U.S. Environmental Protection Agency. Water-quality, bottom-sediment, hydro- geologic, mineralogic, and biota data collected for the detailed study are listed in a repon by Butler and others (1994). Selenium and other trace- constituent data for the soil and alfalfa samples collected in the Uncompahgre Project area are in a repon by Crock and others (1994). Water-extractable data for selenium and other constituents for soil samples are discussed in Stewart and others (1993). Description of Study Area The Uncompahgre Project area and the Grand Valley are located in west-central Colorado (fig. I). The Uncompahgre Project is located along the Uncompahgre River in the lower Gunnison River Basin. The Uncompahgre Project extends about 34 mi between the towns of Colona and Delta (fig. 2). The irrigated part of the Grand Valley is located along the Colorado River, centered around Grand Junction (fig. 3). The confluence of the Gunnison and Colorado Rivers is at Grand Junction (fig. 3). Other communi- ties in the Grand Valley include Palisade and Clifton, east of Grand Junction, and Fruita and Lorna, west of Grand Junction. Physiography, Solis, Climate, and Land Uses The Uncompahgre River Valley principally is an agricultural area where irrigation water is supplied by diversion from the Gunnison River through the Gunnison Tunnel (fig. I) and by water from the Uncompahgre River and its tributaries. About two-thirds of the 86,000 irrigated acres of the Uncompahgre Project is located west of the Uncompahgre River on a series of terraces separated by small valleys that were eroded by tributaries of the Uncompahgre River. The terraces consist of stream deposits and outwash remnants that have relatively low soluble salt content (Bureau of Reclamation, 1984). Irrigated areas east of the Uncompahgre River compose about 34 percent of the project area and consist of soil fonned primarily from weathered Mancos Shale. Soils derived from Mancos Shale commonly are referred to as adobe soils and are high in salt content. Alluvial deposits derived primarily from Mancos Shale compose parts of the Cedar Creek and Loutsenhizer Arroyo Basins (fig. 2). Elevation of irrigated areas in the Uncompahgre Project ranges from about 4,900 ft at Delta to about 5,900 ft near Colona. The approximately 70,000 acres of irrigated land in the Grand Valley are served by Federal and by private irrigation systems. The Federal system serves about 38,000 acres, and the remainder of the irrigated acreage is served by private systems. About 30,000 acres served by the Federal system is located on soils derived from Mancos Shale or from alluvium overlying Mancos Shale between the Colorado River and the Government Highline Canal (fig. 3). The remainder of the Federal system serves irrigated land on Orchard Mesa, a low alluvial terrace located in the southeast part of the Grand Valley (fig. 3). The Grand Valley is relatively flat and gradually slopes upward to the northeast to the Book Cliffs, which are about 1,500 ft above the valley floor. Elevation of irrigated areas in the Grand Valley ranges from about 4,400 to 4,800 ft. Numerous small streams and washes dissect the valley and discharge into the Colorado River. The Uncompahgre Project area and the Grand Valley have an arid to semiarid climate characterized by cool to occasionally cold winters and hot summers. Annual precipitation ranges from about 8 in. at Grand Junction and Delta to 13 in. at Colona. Annual evaporation in both areas is about 50 to 70 in. In most years, snowfall is less than 30 in. The length of the growing season is quite variable in the study area because of local climate variability. The growing season ranges from about 112to 148 days in the Uncompahgre Project area and from about 150 to 190 days in the Grand Valley. Major crops produced are alfalfa, feed corn, hay, small grains, potatoes, beans, onions, fruit, sweet corn, melons, and soybeans. Cattle are wintered at many farms, and there are numerous small call1e- feeding operations and dairies. Urban and residential areas in the Uncompahgre Project area are centered around Montrose, Olathe, and Delta. Considerable urban and residential areas are in the Grand Valley in the vicinity of Grand Junction and Clifton. Some agricultural land in both areas has been sold for rural-residential and commer- cial development. The conversion of agricultural land to nonagricultural uses has been increasing in the study area. 6 Detailed Study 01 SelenIum end Other Con'lIIuont. In Water, Bottom Sedtment, Soli, Allalla, and Biota Alloclal8<l with Irrlgellon O"ln.g. In th. Uncompahgre Project Are. and In the Grand Valley, Weot-Central Cotorado, 1991-93