@misc{indiciae41bbdca72626,
  title = {Physiographic rim of the Grand Canyon, Arizona: A digital database},
  author = {George H. Billingsley and Haydee M. Hampton},
  year = {1999},
  doi = {10.3133/ofr9930},
  url = {https://pubs.usgs.gov/publication/ofr9930},
  note = {Source identifier: ofr9930}
}