@misc{indiciae65176d8e6df2,
  title = {Natural gamma aeroradioactivity map of the Denver area, Colorado},
  author = {Peter Popenoe},
  year = {1965},
  doi = {10.3133/gp505},
  url = {https://pubs.usgs.gov/publication/gp505},
  note = {Source identifier: gp505}
}