This is from Harvard but it reminds me of this (from this post about the Danforth Brook area of Bolton.) The idea of a grouping is re-enforced.
Not counting individual rocks there are six visible structures in this photo forming a sort of "V" with the large rock-on-rock in the foreground as the apex. There may be a few more rock-on-rocks but that is about it. Go all the way to the end of the right-hand side of the "V" to find this pile (behind a small sapling in the above picture)Here is a look back at the large rock-on-rock:You, my collegues, find and show pictures of marvelous rock pile sites. Do you also find these small inconspicuous ones?