And we estimate that there are more than 500 mines that we did not discover yet. The mines the AML cares about range from huge surface mines from the 1950s to small shafts from the late 19 th century. But there are still a lot of safety hazards. Often the ceiling of old horizontal mines is unstable and might fall down. Dangerous gases might develop in old mines and might even be hazardous to people passing by the mine opening.
Vertical shafts can be several hundreds of feet deep.
Once people are trapped in an abandoned mine, there is no natural light and people might get lost in the dark. But not only the underground mines can be dangerous. Small ponds on the bottom of the mines might contain heavily polluted or even poisoned water. The AML gets a fee of 35 cents of every ton of minerals produced in Wyoming. The AML erects barriers, closes old mines and puts up warning signs to increase safety in the historic mines and the surrounding areas.