Radioactive contamination from the Rocky Flats Plant

The Rocky Flats Plant, a former United States nuclear weapons production facility located about 15 miles (24 km) northwest of Denver, Colorado, caused radioactive contamination (primarily from plutonium, americium, and uranium) within and outside its boundaries. The contamination primarily resulted from two major plutonium fires in 1957 and 1969 (plutonium is pyrophoric, and shavings can spontaneously combust) and from wind-blown plutonium that leaked from barrels of radioactive waste.

Source: Wikipedia — Radioactive contamination from the Rocky Flats Plant (CC BY-SA 4.0)