@misc{indiciaeb39327ea604a,
  title = {Geologic map of the Rio Grande Quadrangle, Puerto Rico},
  author = {M. H. Pease and R. P. Briggs},
  year = {1972},
  doi = {10.3133/i733},
  url = {https://pubs.usgs.gov/publication/i733},
  note = {Source identifier: i733}
}