@misc{indiciae39a7e9f97c9d,
  title = {Map of mineral resources, Prince Georges County, Maryland},
  author = {John Tilton Hack},
  year = {1975},
  doi = {10.3133/ofr75210},
  url = {https://pubs.usgs.gov/publication/ofr75210},
  note = {Source identifier: ofr75210}
}