@misc{indiciae8c5a04386098,
  title = {Denver Basin exploration intensity map, Colorado, Nebraska, and Wyoming},
  author = {Debra K. Higley and R. F. Mast and Donald L. Gautier},
  year = {1987},
  doi = {10.3133/ofr8725},
  url = {https://pubs.usgs.gov/publication/ofr8725},
  note = {Source identifier: ofr8725}
}