@misc{indiciae358acd85c8d8,
  title = {Map showing contours on the base of saprolite, Montgomery County, Maryland},
  author = {A.J. Froelich},
  year = {1974},
  doi = {10.3133/ofr74156},
  url = {https://pubs.usgs.gov/publication/ofr74156},
  note = {Source identifier: ofr74156}
}