Small "box" piles on support

I referred to this pile in a comment earlier. So this is for reference, a small rectangular rock piles with hollow, on support from Codman Hill in Harvard (end of Murray Ln):

There were others on Kezar Hill in Shirley. Similar piles are shown from Equinunk PA. Not too different from Brown Hill and Scott Reservoir. Also some in Billerica here (and scroll down).