@misc{indiciaedc627b34ba2a,
  title = {Map showing depth to bedrock, Ludlow Quadrangle, Massachusetts},
  author = {C.J. Londquist and G. W. Leo},
  year = {1974},
  doi = {10.3133/mf503b},
  url = {https://pubs.usgs.gov/publication/mf503B},
  note = {Source identifier: mf503B}
}