@misc{indiciae23acdc8fa2d8,
  title = {General geology of the Harold D. Roberts Tunnel, Colorado},
  author = {Charles Sherwood Robinson and Lawrence Allen Warner and Ernest Eugene Wahlstrom},
  year = {1974},
  doi = {10.3133/pp831b},
  url = {https://pubs.usgs.gov/publication/pp831B},
  note = {Source identifier: pp831B}
}