The quarry, quarrymen, quarry machinery – been there, done that, bought the t shirt. Well, I would have done so, but they don’t sell t shirts when you’re in the middle of a blizzard!
This is a delightful circle. Not easy to locate, but well worth the effort. From the trig point you can see two parts of the same wall, split by some undulation in the terrain. Focus on the part of the wall that you can see to the right, specifically on the leftmost part of that that you can see. Then head towards it – easy.
Just to the right of the circle is a substantial dip. It’s not clear whether this has been quarried or what function it might have performed.