@misc{indiciae872534296e05,
  title = {Coal resources of Colorado, a progress report, January 1, 1953},
  author = {Frank Darwyn Spencer and Margaret Isabelle Erwin},
  year = {1953},
  doi = {10.3133/cir258},
  url = {https://pubs.usgs.gov/publication/cir258},
  note = {Source identifier: cir258}
}