@misc{indiciaee3bbc10012ed,
  title = {Geologic map of the Adjuntas quadrangle, Puerto Rico},
  author = {P.H. Mattson},
  year = {1968},
  doi = {10.3133/i519},
  url = {https://pubs.usgs.gov/publication/i519},
  note = {Source identifier: i519}
}