@misc{indiciae9c07ed69f0e8,
  title = {The COALPROD database; historical production data for the major coal-producing regions of the conterminous United States},
  author = {Robert C. Milici},
  year = {1997},
  doi = {10.3133/ofr97447b},
  url = {https://pubs.usgs.gov/publication/ofr97447B},
  note = {Source identifier: ofr97447B}
}