@misc{indiciae200591360136,
  title = {Map showing thickness of overburden, District of Columbia},
  author = {A.J. Froelich},
  year = {1975},
  doi = {10.3133/ofr75538},
  url = {https://pubs.usgs.gov/publication/ofr75538},
  note = {Source identifier: ofr75538}
}