@misc{indiciae226ae502ff8f,
  title = {Geologic map of the East Portal Quadrangle, Boulder, Gilpin, and Grand counties, Colorado},
  author = {E. J. Young},
  year = {1991},
  doi = {10.3133/i2212},
  url = {https://pubs.usgs.gov/publication/i2212},
  note = {Source identifier: i2212}
}