@misc{indiciaed41e34728237,
  title = {Geologic map of the Heidelberg 7 1/2-minute Quadrangle, east-central Kentucky},
  author = {Douglas F. Black},
  year = {1975},
  doi = {10.3133/ofr7573},
  url = {https://pubs.usgs.gov/publication/ofr7573},
  note = {Source identifier: ofr7573}
}