|Abstract:||The Rawlins area in west-central Carbon County, south-central Wyoming includes approximately 634 square miles of plains and valleys grading into relatively rugged uplifts. The climate is characterized by low precipitation, rapid evaporation, and a wide range of temperature. Railroading and ranching are the principal occupations in the area.
The exposed rocks in the area range in age from Precambrian through Recent. The older formations are exposed in the uplifted parts, the oldest being exposed along the apex of the Rawlins uplift. The formations dip sharply away from the anticlines and other uplifts and occur in the subsurface throughout the remainder of the area.
The Cambrian rocks (undifferentiated), Madison limestone, Tensleep sandstone, Sun dance formation, Cloverly formation, Frontier formation, and Miocene and Pliocene rocks (undifferentiated) yield water to domestic and stock wells in the area. In the vicinity of the Rawlins uplift, the rocks of Cambrian age, Madison limestone, and Tensleep sandstone yield water to a few public-supply wells. The Cloverly formation yields water to public-supply wells in the Miller Hill and Sage Creek basin area. Wells that tap the Madison limestone, Tensleep sandstone, and Cloverly formation yield water under sufficient artesian pressure to flow at the land surface. The Browns Park formation yields water to springs that supply most of the Rawlins city water and supply water for domestic and stock use.
Included on the geologic map are location of wells and test wells, depths to water below land surface, and location of springs. Depths to water range from zero in the unconsolidated deposits along the valley of Sugar Creek at the southern end of the Rawlins uplift to as much as 129 feet below the land surface in the Tertiary sedimentary rocks along the Continental Divide in the southern part of the area.
The aquifers are recharged principally by precipitation that falls upon the area, by percolation from streams and ponds, and by movement of ground water from adjacent areas. Water is discharged from the ground-water reservoir by evaporation and transpiration, by seeps and springs, through wells, and by underflow out of the area.
Although most water supplies in the area are obtained from springs, some domestic, stock, and public supplies are obtained from drilled wells, many yielding water under artesian pressure, and some flowing.
Dissolved solids in the water from several geologic sources, ranging from 181 to 6,660 parts per million (ppm), indicate the varied chemical quality of ground water in the Rawlins area.
Water from the Cambrian rocks, Tensleep sandstone, Cloverly formation, Frontier formation, Browns Park formation, and Miocene and Pliocene rocks is generally suitable for domestic and stock use. However, water yielded to the only well sampled in the lower part of the Frontier formation contained a high concentration of fluoride. Water from the rocks mentioned above contains less than 1,000 ppm of dissolved solids but in some places may contain iron in troublesome amounts. Water from the Madison limestone and Tensleep sandstone combined, Permian rocks, and Sundance formation contains more than 1,000 ppm of dissolved solids. Water in the Sundance, Cloverly, and Frontier :formations is very soft.
More ground water can be obtained in the Rawlins area than is now being used. Many springs are undeveloped, and water can be obtained from additional wells without unduly lowering ground-water levels.