@misc{indiciae7807c4a4977e,
  title = {Preliminary composite magnetic anomaly map of the conterminous United States},
  author = {Isidore Zietz},
  year = {1981},
  doi = {10.3133/ofr811132},
  url = {https://pubs.usgs.gov/publication/ofr811132},
  note = {Source identifier: ofr811132}
}