I followed a group of cavers the first 5700 feet into the Hilltop Mine near Portal Arizona. This shaft was likely used as a service adit for other mine shafts. Already after only 90 years some interesting calcite formations are starting to show.
Mines are dangerous. Several of the team were experienced geologists and mine engineers. I would not recommend trying to visit this site as people disappear in that part of the state all the time. The claim on this mine is held by a private party and we had permission.