@misc{indiciae518000bf06bc,
  title = {Geologic map of the San German Quadrangle, southwest Puerto Rico},
  author = {R.P. Volckmann},
  year = {1984},
  doi = {10.3133/i1558},
  url = {https://pubs.usgs.gov/publication/i1558},
  note = {Source identifier: i1558}
}