Mushroom Cloud Over Vegas

Not from a nuclear attack, but from a 700 ton super-explosive:

The test, code-named Divine Strake, will take place in June in the western U.S. state of Nevada. The military will detonate a 700-ton explosive at a test site in the Nevada desert located about 145 kilometers northwest of Las Vegas.
The weapon consists of a special explosive which will pack the equivalent of more than 500 tons of TNT when it is detonated. It will create a mushroom shaped dust cloud that could reach as high as three kilometers into the air.