Sorry about getting distracted. Here are a few pictures of the mystery circle. The first one is from inside looking more or less north toward the engine house if traces of it could still be found. The metal building would have covered at least part of it by my reckoning. The building wasn't there on my last visit in 2016, but there were no traces of the engine house then either.
This image is looking about NNE from about the middle of the circle. If you look on Google Earth you can see a ridge in the center running to the north. The green bush in the left foreground is the south end of that ridge. In the right background just in front of the bushes is a T-post marking a benchmark. This looks toward the corner of Hyde St. and Railroad St.
A closer view of the benchmark location.
This is the benchmark that, if you know more about surveying or mapping than I do, might give great meaning to the location. The resolution of Google Earth, etc. is too low for me to find it with any confidence on those sites.