@misc{indiciaea79ee2220f79,
  title = {GIS Representation of Coal-Bearing Areas in North, Central, and South America},
  author = {Susan J. Tewalt and Scott A. Kinney and Matthew D. Merrill},
  year = {2008},
  doi = {10.3133/ofr20081257},
  url = {https://pubs.usgs.gov/publication/ofr20081257},
  note = {Source identifier: ofr20081257}
}