@misc{indiciae63dd09f90d5c,
  title = {Geologic map of the Heart Butte NW quadrangle, Morton and Grant Counties, North Dakota},
  author = {E. V. Stephens},
  year = {1970},
  doi = {10.3133/coal52},
  url = {https://pubs.usgs.gov/publication/coal52},
  note = {Source identifier: coal52}
}