@misc{indiciae10cd076c0a52,
  title = {Potassium and thorium maps of the conterminous United States},
  author = {J. S. Duval and W. J. Jones and F.R. Riggle and J. A. Pitkin},
  year = {1990},
  doi = {10.3133/ofr90338},
  url = {https://pubs.usgs.gov/publication/ofr90338},
  note = {Source identifier: ofr90338}
}