Grand Canyon

Due to uranium demand shortly before The War, the U.S. government removed the Grand Canyon's status as a national park and allowed private mining companies to exploit its supply of uranium. The resulting mess was an environmental disaster. As a result, the Canyon has become one of the deadliest places in the wasteland, home to hideous mutant things called molechs, seen nowhere else. Sane people avoid it.

Appearances in games
The Grand Canyon did not appear nor was mentioned (except for a small remark by Harold in Fallout 2) in any of the published games, but was to appear in the cancelled Fallout 3 project by Black Isle codenamed Van Buren. It is not certain if it will appear in any future Fallout game.