@misc{indiciaeb7ed4efa3996,
  title = {Observations of environmental change in Grand Canyon, Arizona},
  author = {Robert H. Webb and Theodore S. Melis and Richard A. Valdez},
  year = {2002},
  doi = {10.3133/wri024080},
  url = {https://pubs.usgs.gov/publication/wri024080},
  note = {Source identifier: wri024080}
}