I was looking at recent images on your blog and spotted the large pile with the retaining wall, and your comment that the graded stones in the center suggests that this pile was the result of field clearing.
There is a large broken down pile in Rochester, VT, which also has a retaining wall around it (not in great shape) and with the center consisting mostly of small stones. This is part of a huge collection of cairns spread over an area of 50+ acres. Many of these cairns seem to have small stones as fill, and so one has to be careful concluding that piles of this sort are the result of field clearing. I don't believe the one I am linking above (from this site in Rochester) has anything to do with field clearing, nor do any of the others. Note the manitou stone in front. There are two views of this pile, one taken from the road and one side view. I believe stones were scavenged from the mound to build the foundation of the farm buildings.