@misc{indiciae7abae6faf88b,
  title = {Permian and Pennsylvanian rocks of southeastern Colorado and adjacent areas},
  author = {John Charles Maher and Jack B. Collins},
  year = {1953},
  doi = {10.3133/om135},
  url = {https://pubs.usgs.gov/publication/om135},
  note = {Source identifier: om135}
}