@misc{indiciaec762c73ad53b,
  title = {Digital computer map showing surface materials, Montgomery County, Maryland},
  author = {J. Nicholas Van Driel},
  year = {1975},
  doi = {10.3133/ofr75419},
  url = {https://pubs.usgs.gov/publication/ofr75419},
  note = {Source identifier: ofr75419}
}