The best factor is avoid known mine areas. In Illinois, there have been over 4,000 mines, and we're in the process of trying to get every mine map that we possibly can and eventually those will be available online. Now they can look at the Illinois Geological Survey.  -   Robert Gibson     Quotes
The best factor is avoid known mine areas. In Illinois, there have been over 4,000 mines, and we're in the process of trying to get every mine map that we possibly can and eventually those will be available online. Now they can look at the Illinois Geological Survey. Robert Gibson