This was a four-year project to locate, map, and test 70 abandoned mill sites in Boulder County, Colorado. Sites were tested for soil radon and radium. ArcView GIS was used to map the sites and link them to a database with location, elevation, soil radon gas, soil radium, evidence of ruins or tailings, soil type, and permeability. Additionally, current and historical photography has been hot linked to the sample sites. Base information including geocoded roads, streams, city limits, lakes, contours, and the county line is in the database. The database has been put on a CD with ArcExplorer so that the general public and other governmental agencies may use it.