@misc{indiciae25914b3059a4,
  title = {National geophysical data grids; gamma-ray, gravity, magnetic, and topographic data for the conterminous United States},
  author = {Jeffrey D. Phillips and Joseph S. Duval and Russell A. Ambroziak},
  year = {1993},
  doi = {10.3133/ds9},
  url = {https://pubs.usgs.gov/publication/ds9},
  note = {Source identifier: ds9}
}