@misc{indiciaef32828901456,
  title = {Aeromagnetic map of the Ashby quadrangle, Middlesex and Worcester Counties, Massachusetts, and Hillsborough County, New Hampshire},
  author = {Members of the Engineering Geology and Ground Water Branches, U.S. Geological Survey},
  year = {1971},
  doi = {10.3133/gp730},
  url = {https://pubs.usgs.gov/publication/gp730},
  note = {Source identifier: gp730}
}