@misc{indiciae67d14bbf39a0,
  title = {Map showing relative ease of excavation of geologic units in the Henrys Lake Quadrangle, Idaho and Montana},
  author = {I. J. Witkind},
  year = {1972},
  doi = {10.3133/i781g},
  url = {https://pubs.usgs.gov/publication/i781G},
  note = {Source identifier: i781G}
}