@misc{indiciae1110bb5c9aae,
  title = {Coal mining in the 21st century: Yampa coal field, northwest Colorado},
  author = {Michael E. Brownfield and Edward A. Johnson and Ronald H. Affolter and Charles E. Barker},
  year = {1999},
  url = {https://pubs.usgs.gov/publication/70068759},
  note = {Source identifier: 70068759}
}