@misc{indiciaee86b4676ea93,
  title = {Coal resource occurrence maps of the Difficulty Quadrangle, Carbon County, Wyoming},
  author = {Texas Instruments Incorporated},
  year = {1978},
  doi = {10.3133/ofr7856},
  url = {https://pubs.usgs.gov/publication/ofr7856},
  note = {Source identifier: ofr7856}
}