@misc{indiciaedea32ece6e8e,
  title = {Geologic and structure contour maps of the northern and western flanks of the Black Hills, Wyoming, Montana, and South Dakota},
  author = {W. J. Mapel and Charles Sherwood Robinson},
  year = {1956},
  doi = {10.3133/ofr5677},
  url = {https://pubs.usgs.gov/publication/ofr5677},
  note = {Source identifier: ofr5677}
}