@misc{indiciaef253ec7b8495,
  title = {History of geologic investigations, engineering design, and construction methods of the Harold D. Roberts Tunnel, Colorado},
  author = {Ernest Eugene Wahlstrom},
  year = {1974},
  doi = {10.3133/pp831a},
  url = {https://pubs.usgs.gov/publication/pp831A},
  note = {Source identifier: pp831A}
}