@misc{indiciae3be0774be7f3,
  title = {Water-level contour maps of the carbonate rocks of the Great Valley in Lehigh County, Pennsylvania},
  author = {H.N. Flippo and C. R. Wood},
  year = {1969},
  doi = {10.3133/ofr6993},
  url = {https://pubs.usgs.gov/publication/ofr6993},
  note = {Source identifier: ofr6993}
}