@misc{indiciae9ed7c2587952,
  title = {Contour map of the base of Saprolite, Howard County, Maryland},
  author = {J.B. Roen and A.J. Froelich},
  year = {1976},
  doi = {10.3133/mf772a},
  url = {https://pubs.usgs.gov/publication/mf772A},
  note = {Source identifier: mf772A}
}