Here is a vertical mine / vent. Almost all of them are blocked by barb wire, but easy to get around. They really should seal them. You can see this one keeps going. We dropped a few rocks and it was a while before they stopped. If you get curious like we did and go past the barb wire barrier, please use extreme caution. The ground may appear steady, but there is lots of soft gypsum in the area. The ground can break lose with very little weight.