@misc{indiciaec28f0c0a6054,
  title = {Geologic map of the Shumla quadrangle, Val Verde County, Texas},
  author = {V. L. Freeman},
  year = {1964},
  doi = {10.3133/i424},
  url = {https://pubs.usgs.gov/publication/i424},
  note = {Source identifier: i424}
}