@misc{indiciae89c4ce9c494f,
  title = {Stratigraphy of Paleozoic rocks in northwestern Colorado},
  author = {Walter E. Hallgarth},
  year = {1959},
  doi = {10.3133/oc59},
  url = {https://pubs.usgs.gov/publication/oc59},
  note = {Source identifier: oc59}
}