@misc{indiciae4e652ecede45,
  title = {Map showing extent, altitude of base, and thickness of Potomac Group in Fairfax County, Virginia},
  author = {J. D. Larson and A.J. Froelich},
  year = {1977},
  doi = {10.3133/ofr77286},
  url = {https://pubs.usgs.gov/publication/ofr77286},
  note = {Source identifier: ofr77286}
}