A common phenomenon near where I grew up in eastern Pennsylvania is the stone root cellar or chamber. Many are disappearing as properties are sold and new houses are built. Since most of them show at least some mortar between stones, it's hard to say when they were built or who built them. Here are two examples, both near streams. The first one, in particular, is in a very low, wet place not a great place for storing root vegetables.
It is at the base of a hill called the Spitzenberg, which has geology so unusual that college geology classes take field trips to it and it is labeled the "Hamburg anomaly" on geology maps. Stone walls are almost entirely absent from the landscape here, but Fred noticed a wall running down the slope of the Spitzenberg, and asked the farmer living there whether there were any old stone structures around. The farmer said, "Well, there's a kind of funny root cellar down there . . . "
I have not been back with a camera, but a friend and I wandered around on the Spitzenberg one day and found some small rock structures.
The second chamber pictured here is not far away from the first, near the base of what local people call the Pinnacle, a place where the Kittatinny Ridge comes to a point, the highest elevation locally, with a large rock outcropping and a well-known, now destroyed, cave. A local legend told of a dragon that flew from caves on the Spitzenberg to the cave on the Pinnacle. There was more, about a tragic young Indian couple. A storied area, at any rate. Whether the chamber/root cellars are connected to any of that I don't know.
What's odd is that people don't think about preserving these things, even if they were just built by German ancestors. They are extraordinary and beautiful structures.