@misc{indiciae51b8542f7be2,
  title = {Principal facts for gravity stations in the area north of the Grand Canyon in Arizona},
  author = {Peter Popenoe},
  year = {1968},
  doi = {10.3133/ofr68217},
  url = {https://pubs.usgs.gov/publication/ofr68217},
  note = {Source identifier: ofr68217}
}