@misc{indiciae3f9d9131b0da,
  title = {Geologic map showing thickness of the upper Cretaceous Pierre Shale in the south half of the Powder River Basin, northeastern Wyoming and adjacent areas},
  author = {M.L. Gibson and G.L. Sims},
  year = {1993},
  doi = {10.3133/i2380b},
  url = {https://pubs.usgs.gov/publication/i2380B},
  note = {Source identifier: i2380B}
}