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Summary Salinity Control Act, and, among other things, authorized the USDA onfarm program. Public Law 98-569 also directed that units will be given preference which reduce salinity at the least cost per unit of salinity reduction (cost effectiveness). Studies for the Unit found that of the project area's annual estimated con- tribution of 430,000 tons of salt, more than half (244,000 tons) is attributable to present irrigation practices as they contribute to ground-water salinity. Of this amount, about 70 percent is attributable to the dissolution of salts from the soil and subsurface materials by deep percolating irrigation water, while 28 percent is attributable to canal seepage, and 2 percent to stock pond seepage. Much of the salt pickup in both rivers' basins is from the dissolution of salts from the soil and subsurface materials, principally from soils formed on and from marine shales, including the Mancos shale fonnation, that underlie much of the area. Deep percolation from irrigation dissolves salts from the soils and shales and conveys them to natural drainages and ultimately the Green and Colorado Rivers. Approximately 92,270 acre-feet of water annually enters the ground-water system in the area. Outflow from the ground-water system consists of consumptive use by phreatophyte wetlands and crops in the area and ground- water return flows to the rivers. Inflows to the project area ground-water system carried about 56,880 tons of salt, while outflows carried approximately 300,880 tons. Watersheds of the Price and San Rafael Rivers drain into the Colorado River via the Green River. The Price River flows southeast from headwaters in the Wasatch and Tavaputs Plateaus, and the San Rafael River flows east from headwaters in the Wasatch Plateau. Within the Price and San Rafael basins, altitude ranges from approximately 4,000 to 10,000 feet above sea level, and vegetation varies accordingly. Most of the project area occurs between 5,500 and 6,000 feet in elevation in the salt- desert shrub zone. This zone receives less than 10 inches of annual precipi- tation and is dominated by communities of native plants associated with salt- bearing soils-shadscale, varieties of saltbush, winterfat, and black greasewood. i i , EXISTING ENVIRONMENT Major communities in the sparsely populated fanning and coal mining area include the largest, Price, population 8,712, in Carbon County; Castle Dale, about 32 miles south of Price in Emery County, population 1,704; and the smaller communities of Huntington, Ferron, Orangeville, and others. Project area population in 1990 was 30,560 according to the Federal census. Major State and Federal highways traverse the area, and Price is served by a small airport and the Denver and Rio Grande Western Railroad which runs from Salt Lake City to Denver. OIJ[ 4:23 5-3