@misc{indiciae3644cb806c06,
  title = {Map showing depths to the Upper Freeport coal bed, mining activity, and related surface subsidence, and the Redstone coal bed mines, Allegheny, Washington, and Westmoreland Counties, Pennsylvania},
  author = {K.O. Bushnell and J.R. Peak},
  year = {1975},
  doi = {10.3133/mf693b},
  url = {https://pubs.usgs.gov/publication/mf693B},
  note = {Source identifier: mf693B}
}