Curious about the abundance of various chemical elements in the area where you live? The U.S. Geological Survey offers a database of more than 60,000 chemical analyses of stream sediment and soil in different parts of the United States. Color-coded maps provide county-by-county data on the concentrations of such elements as mercury, arsenic, selenium, and lead. It’s all part of the National Geochemical Survey.
Go to: http://tin.er.usgs.gov/geochem/doc/home.htm