@misc{indiciae911acedae396,
  title = {Geologic map of the Portage Quadrangle, Cascade and Choteau counties, Montana},
  author = {E. K. Maughan and R. W. Lemke},
  year = {1991},
  doi = {10.3133/i2196},
  url = {https://pubs.usgs.gov/publication/i2196},
  note = {Source identifier: i2196}
}