@misc{indiciae2ea07179feeb,
  title = {Summary of the engineering geology of the Harold D. Roberts Tunnel, Colorado},
  author = {Ernest Eugene Wahlstrom},
  year = {1981},
  doi = {10.3133/pp831e},
  url = {https://pubs.usgs.gov/publication/pp831E},
  note = {Source identifier: pp831E}
}