@misc{indiciae7fa2fe5e90bb,
  title = {Preliminary glacial map of North Dakota},
  author = {R. B. Colton and R. W. Lemke and R. M. Lindvall},
  year = {1963},
  doi = {10.3133/i331},
  url = {https://pubs.usgs.gov/publication/i331},
  note = {Source identifier: i331}
}