@misc{indiciae86e75eb8b3b3,
  title = {Map showing structure contours and overburden thickness isopleths of the Pittsburgh coal bed in Pennsylvania, Ohio, West Virginia, and Maryland},
  author = {Susan J. Tewalt and Leslie F. Ruppert and Linda J. Bragg and Richard Carlton and David Brezinski and Jeanette Yarnell and Rachel N. Wallack},
  year = {1997},
  doi = {10.3133/ofr97864},
  url = {https://pubs.usgs.gov/publication/ofr97864},
  note = {Source identifier: ofr97864}
}