A large hole in the ground in Bisbee, Arizona. Caused by a massive strip mining operation done there by Phelps Dodge. Quite a site (bad pun)- one of the highways goes right by it. If you go there, you can take a mine tour--they get you a helmet-lamp and stuff you in a cart and everything. Highly recommended if you're in the Cochise County area.
Also home to some hideous acidic chemical, which has formed in a pool in the base. I wouldn't go swimming in it.