@misc{indiciae6706eeee0f32,
  title = {Map showing potential sources of gravel and crushed-rock aggregate in the Colorado Springs-Castle Rock area, Front Range urban corridor, Colorado},
  author = {D. E. Trimble and H. R. Fitch},
  year = {1974},
  doi = {10.3133/i857a},
  url = {https://pubs.usgs.gov/publication/i857A},
  note = {Source identifier: i857A}
}