@misc{indiciae044b147e61dc,
  title = {Geologic map of the Colorado Springs - Castle Rock area, Front Range urban corridor, Colorado},
  author = {D. E. Trimble and M. N. Machette},
  year = {1979},
  doi = {10.3133/i857f},
  url = {https://pubs.usgs.gov/publication/i857F},
  note = {Source identifier: i857F}
}