@misc{indiciae62c3f0de1864,
  title = {Map showing mined areas of the Boulder-Weld coal field, Colorado},
  author = {Roger B. Colton and R.L. Lowrie},
  year = {1973},
  doi = {10.3133/mf513},
  url = {https://pubs.usgs.gov/publication/mf513},
  note = {Source identifier: mf513}
}