@misc{indiciae2b0f02e756c7,
  title = {Lithology and aggregate quality attributes for the digital geologic map of Colorado},
  author = {Daniel H. Knepper and Gregory N. Green and William H. Langer},
  year = {1999},
  doi = {10.3133/ofr9929},
  url = {https://pubs.usgs.gov/publication/ofr9929},
  note = {Source identifier: ofr9929}
}