@misc{indiciae156afba1dd1a,
  title = {Map of Polk County, Florida, showing contours on the piezometric surface of the Floridan aquifer},
  author = {Herbert G. Stewart},
  year = {1961},
  doi = {10.3133/ofr61160},
  url = {https://pubs.usgs.gov/publication/ofr61160},
  note = {Source identifier: ofr61160}
}