@misc{indiciaefcc63f7222a9,
  title = {Map showing depths to the Pittsburgh coal bed, mining activity, and related surface subsidence, Allegheny, Washington, and Westmoreland Counties, Pennsylvania},
  author = {K.O. Bushnell},
  year = {1975},
  doi = {10.3133/mf693a},
  url = {https://pubs.usgs.gov/publication/mf693A},
  note = {Source identifier: mf693A}
}