@misc{indiciae9dadc10bcabd,
  title = {Thickness of overburden map, Howard County, Maryland},
  author = {J.B. Roen and A.J. Froelich},
  year = {1978},
  doi = {10.3133/mf772b},
  url = {https://pubs.usgs.gov/publication/mf772B},
  note = {Source identifier: mf772B}
}