@misc{indiciaeab62d8840e0f,
  title = {Colored gravity anomaly and terrain maps of the east-central United States},
  author = {Robert W. Simpson and Richard H. Godson},
  year = {1981},
  doi = {10.3133/ofr81846},
  url = {https://pubs.usgs.gov/publication/ofr81846},
  note = {Source identifier: ofr81846}
}