The principal basin-fill aquifers in Cache Valley, the lower Bear River area, and along the Wasatch Front provide ground water to about 84 percent of the population of Utah. Recharge areas for the principal aquifers were mapped to provide information needed for the implementation of ground-water quality regulations and a State ground-water protection plan. Water samples were collected and analyzed to provide baseline water- quality data for the principal aquifers. The study area includes five subareas: Cache Valley, the 1ower Bear River area, the East Shore area, Salt Lake Valley, and Utah and Goshen Valleys. Basin-fill deposits in each subarea are lithologically heterogeneous. The principal aquifers in most of the subareas are composed of multiple discontinuous unconfined and confined aquifers and confining layers. Primary recharge areas generally are located along adjacent mountain fronts and extend into the valleys at the mouths of major drainages. Secondary recharge areas are located on the benches and uplands of the valleys. Ground-water flow generally is from these recharge areas to the discharge areas in the topographically low parts of the valleys. In general, dissolved-solids concentrations in ground water range from less than 500 mg/L to about 3,000 mg/L. Of 73 water samples, 5 contained inorganic constituents in concentrations that exceeded State of Utah water-quality standards. None of the samples contained concentrations of organic compounds that exceeded State standards.