@misc{indiciaea11041e08554,
  title = {Coal geology and coal, oil, and gas resources of the Erie and Frederick quadrangles, Boulder and Weld counties, Colorado},
  author = {Frank Darwyn Spencer},
  year = {1986},
  doi = {10.3133/b1619},
  url = {https://pubs.usgs.gov/publication/b1619},
  note = {Source identifier: b1619}
}