@misc{indiciaebc8a4a03cfbe,
  title = {Natural aggregates of the conterminous United States},
  author = {William H. Langer},
  year = {1988},
  doi = {10.3133/b1594},
  url = {https://pubs.usgs.gov/publication/b1594},
  note = {Source identifier: b1594}
}