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o '.,.." The Bureau of Reclamation is currently concerned with both salinity contribution to the Colorado River from valley agricultural lands and the damage to the farming industry from salt deposits in these lands. It is currently estimated that the Grand Valley contributes 600,000 tons of dissolved salt annually to the river. Both natural ru.noffs and irrig- ation contribute to the problem, either by salt concentration or by salt loading. Salt concentration is caused by the removal of water from the river system through the consumptive use of irrigated crops and phreatophytes. As this water is lost to the atmosphere, the l1ineral constituents are left behind and become concentrated in the remaining ground water. Besides contributing to the salinity of the river water, this process causes salt deposits to limit the productivity of the soil. Salt loading, on the other hand, occurs as the ground water picks up minerals in the Subsurface materials as it moves down gradient towards the river. Although both processes are at work in the Grand Valley, salt loading appears to be the major cause of the salinity increase in the Cdlorado River as it courses through this area. w ...-j A study of the local geohydrology, which is currently being ~on- ducted by the Bureau of Reclamation in conjunction with other agencies, has added to the understanding of the Grand Valley salt loading problem. Because of the impermeable soils in the area, the years of irrigation have contributed, through canal and lateral seepage and deep percolation, to the development of a large shallow ground water body. The ground water essentially flows toward the Colorado River along the surface of the Mancos Shale bedrock which underlies the valley. As the water travels to the river, it picks up minerals from the soils, and, in areas where soil permeabilities are particularly poor, ground water accumulates and forms a high water table. In such areas, salts become highly concentrated, and capillary action brings 'the salts to the surface leaving a white mineral deposit in many areas. The prime source of the salt is thought to be the marine Mancos Shale Formation and its associated soils. The water is high in calcium and sulfate concentration which indicates a strong connection to the known presence of mineral ,gypsum in the shale. This is the problem to which the Bureau of Reclamation, in conjunction with the Soil Conservation Service, the Agricultural Research Service, the Geological Survey, and local water users, is now addressing itself. Author- ization for development of a program designed to enhance and protect the quality of the water in the Colorado River is derived from the Colorado River Basin Salinity Control Act of June 1974. Soil Conservation Service The Mesa Soil Conservation District was formed'in 1943 and pro- vides a voluntary program in cooperation with the Soil Conservation Service and the Agricultural Stabilization Conservation Service. Needed conservation work has been identified and improvements have been made, based on conservation plans developed by local land users, with technical guidance from SCS. Financial assistance to help carry out these plans has been provided by ASCS in many cases.