7 May

In the 1950s and 1960s, the US was seriously contemplating using nuclear bombs as earth-moving equipment. This was the crater from one of the tests they did, so huge it's now listed as a national monument. The explosion also sent a plume of radioactive fallout 16,000 feet in the air, which then rained down on Iowa, Nebraska, South Dakota and Illinois. The idea was shelved not long afterwards.