@misc{indiciaecec8a42335c3,
  title = {Principal gold-producing districts of the United States},
  author = {Albert Herbert Koschmann and M.H. Bergendahl},
  year = {1968},
  doi = {10.3133/pp610},
  url = {https://pubs.usgs.gov/publication/pp610},
  note = {Source identifier: pp610}
}