@misc{indiciaee7ea13354950,
  title = {Copper in the United States},
  author = {Arthur R. Kinkel and N. P. Peterson},
  year = {1961},
  doi = {10.3133/ofr6184},
  url = {https://pubs.usgs.gov/publication/ofr6184},
  note = {Source identifier: ofr6184}
}