Creative Destruction - Chelmsford Trails Maintenance

Went for a walk east of the Russell Millpond in Chelmsford Town Forest. Only rock piles I saw were in a flat area and I could not make out whether they were rock dumps from field clearing or were something else. All we noticed the trail maintenance people had used rocks from a convenient nearby rockpile to re-enforce their little water management, flow control structures:

[ DAMN! Could not insert photo here. So much for buying an additional 10 gig of space on Picasa! Now I gotta go hassle with that. Sorry for the continued delay in photo postings.]

OK, we're back:Try to figure this one out. Several other low piles were in the area:And an interesting structure or perhaps just a random rock dump.
Which follows something like this pattern front to back: