@misc{indiciae8dade94d0a6e,
  title = {Structure contour map of the base of the Pittsburgh coal bed, southwestern Pennsylvania and northern West Virginia},
  author = {John B. Roen and Deborah E. Farrel},
  year = {1980},
  doi = {10.3133/coal88},
  url = {https://pubs.usgs.gov/publication/coal88},
  note = {Source identifier: coal88}
}