@misc{indiciaec8d23a865293,
  title = {Aeromagnetic map of the Ashburnham quadrangle, Worcester and Middlesex Counties, Massachusetts, and Cheshire and Hillsborough Counties, New Hampshire},
  author = {Members of the Engineering Geology and Ground Water Branches, U.S. Geological Survey},
  year = {1971},
  doi = {10.3133/gp729},
  url = {https://pubs.usgs.gov/publication/gp729},
  note = {Source identifier: gp729}
}