@misc{indiciae56a86d7a9971,
  title = {Aeromagnetic map of parts of the Gloucester and Rockport quadrangles, Essex County, Massachusetts},
  author = {Members of the Engineering Geology and Ground Water Branches, U.S. Geological Survey},
  year = {1970},
  doi = {10.3133/gp724},
  url = {https://pubs.usgs.gov/publication/gp724},
  note = {Source identifier: gp724}
}