@misc{indiciaec96b1c9e35b7,
  title = {Maps showing the extent of mining, locations of mine shafts, adits, air shafts, and bedrock faults, and thickness of overburden above abandoned coal mines in the Boulder-Weld coal field, Boulder, Weld, and Adams Counties, Colorado},
  author = {S. B. Roberts and J. L. Hynes and C. L. Woodward},
  year = {2001},
  doi = {10.3133/i2735},
  url = {https://pubs.usgs.gov/publication/i2735},
  note = {Source identifier: i2735}
}