The water resources were studied within an area whose natural ground water flow is largely towards the center of the metropolitan area. This area coincides with the extent of the Hinckley Sandstone Aquifer. Thus, the general geohydrology of the area bounded by the extent of the Hinckley Sandstone (about 6,000 square miles) as it relates to the hydrology of the Minneapolis-St. Paul metropolitan area is described. Greater emphasis is placed on the area underlain by the Prairie du Chien-Jordan aquifer (about 2,000 square miles), from which approximately 75 percent of the ground-water for the metropolitan area is pumped. The study indicates that the surface water resources of the Twin Cities metropolitan area are used to such an extent that a supply adequate for domestic and industrial needs as well as power plant and sanitary effluent assimilation will not be available during severe drought. Ground water is obtained primarily from two aquifer systems: The Prairie du Chien-Jordan and the Mount Simon-Hinckley. In 1970, these aquifers supplied about 90 percent (175 mgd) of the ground water used in the metropolitan part of the study area. The probable level of development that can be sustained by these two aquifers in the metropolitan area is estimated to be 1,100 mgd; thus, substantial additional ground water supplies could be developed. However, considerable management and planning would be needed to sustain this level of development. Maps in this report can be used to select general well-field locations based on consideration of 1) aquifer, 2) depth needed for completion; 3) head availability, 4) location of natural recharge and discharge boundaries, and 5) distance from areas where over-development of ground-water resources is imminent. Because of complexities in the ground-water system, yield estimates, boundary effects, and effects of aquifer interaction may best be determined in a study incorporating the use of a hydrologic model.