This digital geospatial data set consists of structure contours of the base of the Laramie-Fox Hills aquifer and the base of the Arapahoe aquifer along the Front Range of Colorado. The U.S. Geological Survey developed this data set as part of a project described in the report, "Structure, Outcrop, and Subcrop of the Bedrock Aquifers Along the Western Margin of the Denver Basin, Colorado" (Robson and others, 1998).