@misc{indiciae4633e9c2a30b,
  title = {Thickness of overburden map of Montgomery County, Maryland},
  author = {A. J. Froehlich},
  year = {1975},
  doi = {10.3133/i920b},
  url = {https://pubs.usgs.gov/publication/i920B},
  note = {Source identifier: i920B}
}