@misc{indiciaeb672c361f851,
  title = {Geology of the Aspen mining district, Colorado, with atlas},
  author = {Josiah Edward Spurr},
  year = {1898},
  doi = {10.3133/m31},
  url = {https://pubs.usgs.gov/publication/m31},
  note = {Source identifier: m31}
}