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I I I I I I I I The rocks of the Green River Basin are a succession of fluvial (Wasatch and Bridger Formations) and lacustrine (Green River Formation) sediments, Erosion of the surrounding uplands resulted in thick deposits in the extensive alluvial plain and the lake, known as Lake Gosiute, within this intermontane basin. Fluctuations in the size of the lake resulted in the intertonguing of the Green River Formation with the Wasatch and Bridger Formations (see Figure 2-1), During deposition of the Green River Formation, the climate fluctuated from humid to arid and back to humid again. During the arid time, the lake was much smaller and did not have an outlet which resulted in saline conditions. The Wilkins Peak Member is a thick sequence of carbonates with numerous occurrences of trona and saline evaporite deposits. As the climate got more humid, fresh water conditions again prevailed. Lake Gosiute reached its maximum size at that time and the thick shale deposits of the Laney Member were deposited. I As sediments filled Lake Gosiute, fluvial deposits of the Bridger Formation covered the Green River Formation. The environment during deposition of the Bridger was such that gypsum and salt were deposited in the contact zone with the Wilkins Peak Member of the Green River Formation. I I I I I I I I I I Excessive irrigation from the project area results in deep percolation in the contact zone of the Bridger and Wilkins Peak around the margins of the prehistoric lake. This allows ground water recharge that can not only interact with the salts in the Bridger Formation, but can reach and interact with the saline facies in the Wilkins Peak Member. This interaction can result is high salt loading to the underground aquifer. The saline aquifer water is discharged into the Big Sandy River via seeps, springs, and uncapped wells between the irrigation project area and Gasson Bridge stream gauging station. Soils A detailed soil survey was conducted on the original Bureau of Reclamation withdrawal area of the Eden project during the early 1950's, Detailed surveys were again completed on most of the deeded lands in the 1960's, which were revised and the area completely soils mapped during 1982-84. A soil survey publication of lands within the boundaries of the Eden Valley Irrigation and Drainage District is at present in the process of being published. A very general soils investigation of the entire Big Sandy watershed was conducted during 1975-76 cooperatively by the Bureau of Land Management and the Soil Conservation Service. Discussion of soils in this report is limited to the Eden Valley irrigation area. A General Soils Map with brief descriptions can be found on page 2-7, Figure 2-2. "\ . (".., UJ\...,;S I 2-4