@misc{indiciaeaae2e931d8ff,
  title = {Hydrologic Unit Map -- 1974, states of Maryland and Delaware},
  author = {Members of the Engineering Geology and Ground Water Branches, U.S. Geological Survey},
  year = {1974},
  doi = {10.3133/hu20},
  url = {https://pubs.usgs.gov/publication/hu20},
  note = {Source identifier: hu20}
}