@misc{indiciaee082ef8a6583,
  title = {Map showing relative ease of excavation in the Aspen Quadrangle, Pitkin County, Colorado},
  author = {Bruce Bryant},
  year = {1972},
  doi = {10.3133/i785c},
  url = {https://pubs.usgs.gov/publication/i785C},
  note = {Source identifier: i785C}
}