What are the cone shaped hills in Campbell County?
The cone shaped hills consist of clinker, a tough, weather resistant rock that forms when coal deposits catch fire. The heat from the combusting coal melts the overlying sediments and it bakes and fuses them. Given the prolific nature of coal in the Powder River Basin much of this coal has caught fire as erosive forces exhumed and exposed the coal outcrops. Sometimes the fires are started by lightning and sometimes the fire starts from the spontaneous combustion of coal in the outcrop. The spontaneous combustion occurs when the exposed coal is first dehydrated (loses most of its moisture), then when the coal is rehydrated the interaction between the water and the carbon in the coal react and create heat, this process is called pyrophoricity. Cap rocks sometimes form over the burning fires.

Because of the nature of clinker, the surrounding softer sediments erode more quickly and the clinker remains. The cones are what are left from the surface eroding into the gullies. The shape of the hills is related to how the coal burns in the subsurface, most natural coal fires can burn a few hundred feet back behind the outcrop and provided the correct conditions one area will burn hotter than adjacent areas.

Show All Answers

1. What is the Rockpile?
2. How do I sign up a class or group to tour the museum?
3. How do I get copies of historic photos?
4. How did Campbell County get its name?
5. What is the doughnut shaped rock?
6. Why the camel as the high school mascot?
7. What are the cone shaped hills in Campbell County?