@misc{indiciae3193d2b19eba,
  title = {Geologic map of the Gurabo Quadrangle, Puerto Rico},
  author = {V.M. Seiders},
  year = {1971},
  doi = {10.3133/i657},
  url = {https://pubs.usgs.gov/publication/i657},
  note = {Source identifier: i657}
}