Rock Pile Sites in northwestern Willard Brook State Forest and Adjacent - Part 1

I described seeing an "oven" at place 'a' up from Valley Rd in Ashby MA. But I got home and realized that -really- I had not explored correctly or thoroughly - I had mistakenly followed a dirt road and not the brook and had ignored entire slopes of the hills. So I went back to follow the brook more carefully upstream and found rock piles at 'b' and 'c'. There is the thrill of the discovery and of the successful hunt. But there is also some mystery here, especially at 'c'.
At first, the site at 'b' is barely visible as you climb briefly on the slope below the field and above the brook. At first the impression is faint:

But It got more and more concrete as I followed a small gully upward:

Here is the view back down towards the main brook from the top of the gully:

 

I'll report on 'c' separately.