@misc{indiciae61a8419ba5e7,
  title = {Filtered magnetic anomaly maps of Illinois},
  author = {T.G. Hildenbrand and R.P. Kucks},
  year = {1992},
  doi = {10.3133/gp999},
  url = {https://pubs.usgs.gov/publication/gp999},
  note = {Source identifier: gp999}
}