What is the rainfall of this region? What areas are prone to periodic flooding? What is the water supply? What is the chemical quality of the ground water and water in the streams? How deep is the water table? Which streams are gaged, and where? These and similar questions are being asked regularly by land and resource developers, urban planners, industrial consultants, and governmental resource managers. This map provides the first step toward answering these questions. It shows by symbols and color the hydrologic data published as of January 1974 for the Greater Denver area by the U.S. Environmental Data Service and by the U.S. Geological Survey and cooperating agencies, and the points or areas where these data have been collected. The sources of the data are given in both the following discussion and the references.