Groundwater is one of Utah 's most extensive and valuable natural resources. Because of its widespread occurrence in both wet and dry areas, groundwater has been, and is a major factor affecting economic growth and development of the State. In some areas, groundwater is used to supplement streamflow for irrigation, public supply, and other uses. In other areas, it is the only water available for use. The U.S. Geological Survey, under cooperative programs with the Utah Department of Natural Resources and other Federal, State, and local agencies has been studying Utah 's groundwater resources since 1987. Much information has been gained during those studies about the occurrence, availability, and quality of groundwater; the withdrawal and use of the water; and the effects of withdrawal. This report summarizes that information in nontechnical language , which is designed for all readers. (Lantz-PTT)