@misc{indiciae5ccc0a8fb4d7,
  title = {Isopach maps of overburden on the Pittsburgh coal bed in southwestern Pennsylvania and northern West Virginia},
  author = {Bion H. Kent},
  year = {1974},
  doi = {10.3133/ofr74132},
  url = {https://pubs.usgs.gov/publication/ofr74132},
  note = {Source identifier: ofr74132}
}