Former Titan II Missile Silo. On September 19th 1980 a dropped wrench punctured a fuel tank. Hours later it blew with such force that the 740 ton silo lid was blown off and the warhead (relatively undamaged) landed 600 feet away.
Brian -- Note for the future -- The idea is to make an obscure reference to the answer so that there is some opportunity for several people to solve the puzzle. At some arbitrary point, it is declared solved. When I think that has happened, I update the summary thread.