The northern San Rafael Swell area in southeastern Utah includes about 2,880 square miles (7,460 square kilometers) and ranges in altitude from about 3,290 to 7,921 feet (1,195 to 2,414 meters). Precipitation, the main source of water in the area, ranges from slightly less than 6 inches (152 millimeters) to slightly more than 12 inches (305 millimeters). Rocks that underlie the area range from Precambrian to Holocene in age. The thickness of sedimentary rocks ranges from 4,083 feet (1,244 meters) to about 30,000 feet (9,140 meters). The Entrada, Navajo, Wingate, and Coconino Sandstones and rocks of Mississippian age are considered major aquifers because of their large areal extent or thickness. Their water-yielding ability is affected mainly by faulting and folding which locally enhance ground-water circulation by fracturing, or impede circulation by offsetting the more permeable beds. Water in these aquifers ranges from fresh to briny. The total hydrologic system in the northern San Rafael Swell area has an estimated average annual inflow and outflow of about 1.3 million acre-feet (1,600 cubic hectometers), of which about 1.15 million acre-feet (1,420 cubic hectometers) is derived from precipitation on the area. An estimated 99 percent of the water available to the area is consumed by evapotranspiration.
United States Geological Survey, "Bedrock Aquifers in the Northern San Rafael Swell Area, Utah, with Special Emphasis on the Navajo Sandstone" (1982). All U.S. Government Documents (Utah Regional Depository). Paper 274.