@misc{indiciae008bfa013e27,
  title = {Element concentrations in soils and other surficial materials of the conterminous United States},
  author = {Hansford T. Shacklette and Josephine G. Boerngen},
  year = {1984},
  doi = {10.3133/pp1270},
  url = {https://pubs.usgs.gov/publication/pp1270},
  note = {Source identifier: pp1270}
}