@misc{indiciae37d30756444c,
  title = {Geologic map showing total thickness of coal in the north half of the Powder River basin, southeastern Montana and northeastern Wyoming},
  author = {N.M. Denson and B.L. Crysdale},
  year = {1991},
  doi = {10.3133/i2131a},
  url = {https://pubs.usgs.gov/publication/i2131A},
  note = {Source identifier: i2131A}
}