Showing off some favorite piles

Walking with FFC in northern Westford. Here are some favorite piles I wanted to show him. Here is one of my all-time favorites (I think I posted another of picture of this some time in the past):
Here is a detail, showing a white "window".
Here are some others from the same northwestern hill shoulder:
This is part of a what I call a "marker pile site" because some of the piles are evenly spaced and in lines. On the other hand these large boulder piles are probably not in line and, although it is possible, I do not think anyone moved the boulders in order for the piles to be "just so".