I had exactly the same thought, and was quite intrigued. Very disappointed actually, it would be cool if there was open data about land mines.

The US government has been pretty good about cleaning up the UXO it knows about, which means what's left is the UXO it doesn't know about. You'll find it near most of the current and former testing ranges, particularly Yuma Proving Ground where there's trails leading right from the adjacent BLM land into areas with potential UXO. The only real barriers are a few signs and the law.