@misc{indiciae21a889e4dd2c,
  title = {Map of coal-mining features, Allegheny County, Pennsylvania},
  author = {W.E. Davies and J. S. Pomeroy and W. R. Kohl},
  year = {1976},
  doi = {10.3133/mf685c},
  url = {https://pubs.usgs.gov/publication/mf685C},
  note = {Source identifier: mf685C}
}