@misc{indiciaeacc4c6135813,
  title = {Surface materials map of Montgomery County, Maryland},
  author = {A. J. Froehlich},
  year = {1975},
  doi = {10.3133/i920a},
  url = {https://pubs.usgs.gov/publication/i920A},
  note = {Source identifier: i920A}
}