@misc{indiciae6ac5c92aefb0,
  title = {Preliminary composite magnetic anomaly map of the conterminous United States},
  author = {Isidore Zietz},
  year = {1981},
  doi = {10.3133/ofr81766},
  url = {https://pubs.usgs.gov/publication/ofr81766},
  note = {Source identifier: ofr81766}
}