I am going to be insufferably cocky about this one. Even driving east on Rt 2A, from Concord into Lincoln, there is a place you can see a rock-on-rock from the road. But it is so minor you cannot be sure it is any kind of remnant of the ceremonial. But you pass a dip where you can see the boardwalk to the north and a breakout zone jungle to the right and I have been thinking for years that I should really explore that breakout zone again. This is the very earliest part of Elm Brook. Of course I checked it out years ago but that was before I knew how to look for things, so I thought it would be worth another look. There, with the sound of Rt 2A traffic in the background in a little swampy area behind park and the houses, there do remain some genuine traces of the ceremonial. Nobody goes in there these days and probably it has never been very busy in there. And so you have these things where no one would dream of there still being traces of the Native Americans. Even so, there was not much, just a split-wedged rock:[Had to use the flash. It was raining harder and harder as I proceeded.]
Also a little remnant rock pile next to a big boulder in there: Looking at the map fragment I can see there is quite a lot more territory to explore in there (I stopped early cuz of the rain). Think of this as you drive past.