@misc{indiciaec0581e190626,
  title = {Tertiary volcanic stratigraphy in the Powderhorn-Black Canyon region, Gunnison and Montrose Counties, Colorado},
  author = {Jerry Chipman Olson and David Carl Hedlund and Wallace R. Hansen},
  year = {1968},
  doi = {10.3133/b1251c},
  url = {https://pubs.usgs.gov/publication/b1251C},
  note = {Source identifier: b1251C}
}