The difficulty with this spot is several-fold: first, with all the young trees coming up back in the notch, it looks more like an area to avoid than an area to explore. Second, all that brush obscures much of what you might want to be looking at- it's not obvious from out by the road and pull-out that there even is anything to see under all the foliage. Third, the moist, shady conditions under all that cover means that moss, lichen, and algae have rendered all the colors a sort of muddy, muted greenish- distinctions have been largely suppressed. Finally, because it's all so, well, dull, I didn't get very many pictures except of the wall itself. Dana got a few more, though, and this is one of hers. I'll forgo a description here, and leave it to the reader to see if they can spot a tell-tale clue to the wall's genesis.
Photo by Dana Hunter, unmodified. May 6, 2013. Location uncertain, but maybe here. (That seems closer to Harlan than I remember, but it's the only spot that even looks like a possible match)