During July, 1997, twenty four Schlumberger dc resistivity soundings were made in the Boulder watershed and adjacent areas (fig. 1). The objective of geophysical studies in the watershed is to map subsurface lithologic, structural and hydrologic features important in controlling possible ground water contamination from mining activities and for design of remediation efforts. These studies are part of an abandoned mine land study (http://amli.usgs.gov/amli/ ) of the Boulder Basin mining district ( http://www.deq.state.mt.us/mtmines2/linkdocs/techdocs/73tech.html ).