@misc{indiciaefe0f1dd65e1a,
  title = {Map showing coal resources of Montana},
  author = {John Xavier Combo and Clifford N. Holmes and H. Reed Christner},
  year = {1950},
  doi = {10.3133/coal2},
  url = {https://pubs.usgs.gov/publication/coal2},
  note = {Source identifier: coal2}
}