@misc{indiciaebcd5697f6b59,
  title = {Aeromagnetic map of Iowa: Color coded intensities},
  author = {Isidore Zietz and F. P. Gilbert and J. R. Kirby},
  year = {1976},
  doi = {10.3133/gp911},
  url = {https://pubs.usgs.gov/publication/gp911},
  note = {Source identifier: gp911}
}