@misc{indiciae1e0d33140ff6,
  title = {Map showing total thickness of Mississippian rocks in the conterminous United States},
  author = {Members of the Engineering Geology and Ground Water Branches, U.S. Geological Survey},
  year = {1972},
  doi = {10.3133/ofr72406},
  url = {https://pubs.usgs.gov/publication/ofr72406},
  note = {Source identifier: ofr72406}
}