@misc{indiciae6069132c33ed,
  title = {Map showing construction materials and nonmetallic mineral resources of Nebraska},
  author = {Ralph W. Richards and R. A. Weeks and D. M. Larrabee},
  year = {1948},
  doi = {10.3133/mb15},
  url = {https://pubs.usgs.gov/publication/mb15},
  note = {Source identifier: mb15}
}