http://en.wikipedia.org/wiki/DownwindersThe threat of downwind exposure to radioactivity remaining at the Nevada Test Site from nuclear weapons tests was still an issue as late as 2007. The Pentagon planned to test a 700-ton ammonium nitrate-and-fuel oil "bunker buster" weapon. The planned "Divine Strake" test would have raised a large mushroom cloud of contaminated dust that could have blown toward population centers such as Las Vegas, Boise, Salt Lake City, and St. George, Utah. This project was cancelled in February of 2007 in large part due to political pressure inspired by the the threat of downwind exposure to radioactivity.