@misc{indiciaeb64662584d11,
  title = {Summary map of mined areas and areas of potential coal mining, southwestern Pennsylvania},
  author = {W. R. Kohl and R. P. Briggs},
  year = {1976},
  doi = {10.3133/mf729},
  url = {https://pubs.usgs.gov/publication/mf729},
  note = {Source identifier: mf729}
}