@misc{indiciae8d3898037302,
  title = {Map of locations of collapse-breccia pipes in the Grand Canyon region of Arizona},
  author = {Hoyt B. Sutphin and Karen J. Wenrich},
  year = {1989},
  doi = {10.3133/ofr89550},
  url = {https://pubs.usgs.gov/publication/ofr89550},
  note = {Source identifier: ofr89550}
}