@misc{indiciae031d5446d3bc,
  title = {Geologic map showing total thickness of coal in the south half of the Powder River basin, northeastern Wyoming},
  author = {N.M. Denson and B.L. Crysdale},
  year = {1991},
  doi = {10.3133/i2131b},
  url = {https://pubs.usgs.gov/publication/i2131B},
  note = {Source identifier: i2131B}
}