Digital data set describing ground-water regions with unconsolidated watercourses in the conterminous US

This data set describes ground-water regions in the United
States defined by the U.S. Geological Survey. These
ground-water regions are useful for dividing the United States
into areas of roughly similar hydrologic characterstics and
water-use patterns. Most of these regions are very generalized
and were developed from a illustration published at a scale of
approximately 1:20 million. The data set also includes
polygon features for unconsolidated watercourses taken from
1:7,500,000-scale U.S. Geological Survey map of productive
aquifers.