The artesian Casper aquifer, comprised of 700 ft. of interbedded limestones and sandstones, currently supplies 70 percent (3.5 Mgal/d) of the municipal water needs of Laramie, Wyoming. Large transmissivities occur in fracture zones associated with faults and folds in the area, and water discharges from several springs localized along these structures. Transmissivities in fracture zones are 100 times greater than those in unfractured parts of the aquifer. The overlying Satanka Shale is a regional confining unit even in most areas of fracturing, and is a source of poor quality ground water. Prospecting for new ground-water supplies near Laramie involves mapping the tectonic structures and drilling into them once they are identified.