@misc{indiciaea8facb789c9c,
  title = {Preliminary map showing sand and gravel deposits of Colorado},
  author = {Helen D. Varnes and D. M. Larrabee},
  year = {1946},
  doi = {10.3133/mb2},
  url = {https://pubs.usgs.gov/publication/mb2},
  note = {Source identifier: mb2}
}