The NH Stone Wall Mapping program is an online project that enables people to identify stone walls through LIDAR images of the area. From that moment on, they have found 12,700 miles of walls across New Hampshire. (I wrote about the project a year ago)

(Only Strafford County on the seashore has very few walls. I wonder if this is a function of the type of agriculture that was practiced there, the type of rock found there, or just an accident of who attended.)

It is not clear how many miles of stone walls exist in the state. The best estimate I’ve made is for the whole of New England and New York State of about 250,000 miles in 1871 when agriculture changed, largely because railroads made it possible to move food from the Ohio River Valley to the east coast . So the farmers moved west to more fertile soil. After that, relatively few walls were built and many were torn down or moved.

My guess is that New Hampshire had at most a fifth of those walls from 1871, which would be 50,000 miles. So we are a quarter of the way there!

Note that these walls have not been confirmed on the floor. They have been identified by their appearance on LIDAR. So we shouldn’t focus too much on numerical details: I’m sure that some of the “walls” found are actually old roads or earth benches or other false positives.