@misc{indiciae761211899ae3,
  title = {Digitizing procedure for the National Coal Resources Data System of the U.S. Geological Survey},
  author = {Judy F. Hunter and Sharon S. Crowley and Antoinette L. Medlin},
  year = {1981},
  doi = {10.3133/ofr811225},
  url = {https://pubs.usgs.gov/publication/ofr811225},
  note = {Source identifier: ofr811225}
}