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':CO:) ''J'' ,..~ ..-4 Irrigation in the val ley began in 1882 with the construction of what is now the Grand Valley Canal (Grand Valley Irrigation Company). Other private systems were built during the period between 1882 and 1908. Construction of the last major system, the Grand Valley Project under the Reclamation Service, began in 1908 with major construction completed in 1926. This project consists of two divisions, the Garfield Gravity and the Orchard Mesa Divisions, on the north and south sides of the river, respectively. ;,.,.. SOilS The Soils of this general area are derived from the Mancos Shale for- mation. The Mancos Shale is a marine formation consisting of 3,000 to 5,000 feet of relatively uniform silty clay shale with veinlets of gypsum, calcite, and sodium sulphate. Ground water percolating over and through the shale picks up high concentrations of salt which are trans- ported to the Colorado River through wasteways, ditches, or by natural ground water movement to the river. Because of the arid climate, these salts have not been leached naturally, and high quantities remain. lenses of white crystall ine salts are often exposed during excavation operat ions. The Soil Survey of the Grand Junction Area (issued 1955) covers 121,600 acres, including the irrigated land within the boundaries of the irriga- tion canal system. The soils as described in this survey are typical of desert soils -- they are low in organic matter, high in weatherab1e minerals and associated salts and are chemically similar to the geologic materials from which they were derived. Extensive field and laboratory checking of salinity during progress of the survey found about one-third of the area was affected by accumulations of salts or alka1 i; and that sodium sulfate is by far the most prevalent so I ub 1 e sa 1 t. Strongly sal ine Cretaceous formations (primarily Mancos shale) dominate the parent material of the area, with approximately 78 percent of the area having soils directly related to the Mancos shale. The deep Fruita, Genola, Green River, Hinmon, Mesa, Naples, and Thoroughfare soils which are formed in mixed material of other than Mancos shale amount to about 22 percent of the area. Of those soils directly related to the Mancos shale the shallow Chipeta and Pe rsayo so i 1 s and the moderate 1 y deep phases of the Fru i ta and Mesa soils resting on Mancos shale amount to 31 percent of the total area. The deep Bill i ngs (29%), Mack (3%) and Ravo 1 a (15%) 50 i 1 s deve loped in alluvium from the Mancos shale comprise about 47 percent of the total area. 12