@misc{indiciaed715f408341a,
  title = {Geologic map of the Heart Butte quadrangle, Morton and Grant Counties, North Dakota},
  author = {E. V. Stephens},
  year = {1970},
  doi = {10.3133/coal53},
  url = {https://pubs.usgs.gov/publication/coal53},
  note = {Source identifier: coal53}
}