@misc{indiciae7e20748a2d62,
  title = {Map showing thickness of overburden, Montgomery County, Maryland},
  author = {A.J. Froelich},
  year = {1974},
  doi = {10.3133/ofr74155},
  url = {https://pubs.usgs.gov/publication/ofr74155},
  note = {Source identifier: ofr74155}
}