@misc{indiciaec275fd5d4cdb,
  title = {Geologic and structure contour map of the northern and western flanks of the Black Hills, Wyoming, Montana, and South Dakota},
  author = {W. J. Mapel and Charles Sherwood Robinson and P. K. Theobald},
  year = {1959},
  doi = {10.3133/om191},
  url = {https://pubs.usgs.gov/publication/om191},
  note = {Source identifier: om191}
}