@misc{indiciae22b1f18aeacf,
  title = {Map showing relative excavatability of geologic materials in the Parker quadrangle, Arapahoe and Douglas Counties, Colorado},
  author = {J. O. Maberry},
  year = {1972},
  doi = {10.3133/i770h},
  url = {https://pubs.usgs.gov/publication/i770H},
  note = {Source identifier: i770H}
}