@misc{indiciae22dac687184e,
  title = {Structure contour map of the Pittsburgh coal bed, southwestern Pennsylvania and northern West Virginia},
  author = {John B. Roen and Deborah E. Farrel},
  year = {1973},
  doi = {10.3133/ofr73244},
  url = {https://pubs.usgs.gov/publication/ofr73244},
  note = {Source identifier: ofr73244}
}