@misc{indiciaee08442a51c42,
  title = {Map showing areas that correlate with subsidence events due to underground mining in Armstrong, Beaver, and Butler Counties, Pennsylvania},
  author = {K.O. Bushnell and R. P. Briggs},
  year = {1976},
  doi = {10.3133/mf693d},
  url = {https://pubs.usgs.gov/publication/mf693D},
  note = {Source identifier: mf693D}
}