Abstract

Consolidated rocks and unconsolidated basin fill in northwestern Utah and adjacent parts of Idaho and Nevada contain ground water, but most of the water that can be withdrawn from wells is in the basin fill. A regional flow system exists in consolidated carbonate rocks of Paleozoic age in the southern one-half of the area; but few data are available for defining this system and little is known about precise areas of recharge or the movement of water to the large springs that are known points of discharge.

Recharge to the basin fill is by seepage from streams, subsurface inflow from consolidated rock at basin margins, infiltration of excess irrigation water, and subsurface in flow from outside the area. The annual recharge is about 350,000 acre-ft.

Ground water generally moves from uplands and basin margins toward basin lowlands, where it discharges. The major types of discharge include transpiration and evaporation, springflow and withdrawals from wells, and subsurface outflow. All ground water that is not discharged by other means moves to the Great Salt Lake Desert, Great Salt Lake, or the play a in Pilot Valley. The annual discharge for the area is about 365,000 acre-ft.

Ground water is fresh in much of Snake, Deep Creek, and Grouse Creek Valleys and in the higher parts of Curlew and Park Valleys. Water under the Great Salt Lake Desert, the playa in Pilot Valley, and adjacent lowlands is moderately saline to briny.

The salt crust of the Bonneville Salt Flats decreased in area and thickness between 1925 and 1976. These changes were caused by re-solution of salt because of greater than average precipitation during 1962-76 and resulting ponding of water, including ponds behind man-made barriers, and because of withdrawals of brine by collection ditches for production of potash.