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0). ~ b o o o . , ,-, Agriculture, primarily cash and forage crops and livestock produc- tion, is the principal industry in the Grand Valley and essentially the only industry in the Stage One area. Approximately 71,000 acres of crop- land are irrigated in the valley, including 6,300 acres in the Stage One area. Corn, small grains, and alfalfa are the principal crops produced in the valley and the Stage One area. 4. Water Resources The principal sources of water in the Grand Valley are the Colorado and Gunnison Rivers, which join at Grand Junction. Minor amounts of run-' off from the north and the south enter the Colorado River through numerous small, mostly intermittent, tributaries. The Stage One area is drained by Reed Wash and its tributaries Peck and Beede Wash and East Branch Reed Wash, and by Mack Wash, a tributary of Salt Creek. These tributaries pick up saline water supplies from canal and lateral seepage and irrigation return flows and carry them into the Colorado River. Approximately 5,800 acre-feet of water enter the ground water system annually as seepage from the Stage One area, including 4,100 acre-feet from the Government Highline Canal and 1,700 acre-feet from the laterals. As this water seeps through the Mancos Shale, the salinity concentration increases from about 460 mg/L as it enters the ground to about 4,410 mg/L as measured in wells in the area, a difference of 3,950 mg/L or 5.37 tons per acre-foot. Based on the amount of seepage and the change in salinity concentration an estimated 31,000 tons of salt are picked up annually in the Stage One area. In addition, an estimated 17,000 tons are picked up from on-farm sources of ground water, deep percolation, and ditch seepage. The salinity level of the Colorado River as it. enters the valley at Cameo averages 397 mg/L. The inflows of Plateau Creek and the Gunnison River have average salinities of 305 and 654 mg/L, respectively. When flows reach the Colorado-Utah state line the average salinity in the Colorado River is around 571 mg/L. The salinity level at Imperial Dam is 1,102 mg/L based on actual measurements and calculated contributions of projects now under construction. There are no natural lakes in the Grand Valley but the man-made Mack Mesa and Highline Lakes northwest of the Stage One area have been con- structed in recent years. These lakes are operated by the State of Colo- rado as recreation and waterfowl management areas. Water use in the Stage One area is limited to irrigation of about 6,300 acres and is delivered by the Government Highline Canal, which diverts water from the Colorado River. The canal extends westward from the diversion for about 54 miles and terminates a few miles west of the Stage One area. The canal and most of the laterals are open earth chan- nels in contact with uncompacted soil or weathered Mancos Shale. As a result, in some areas the banks are badly eroded and the channels enlarged. Large amounts of water are lost as seepage which dissolves B-2