I thought this might fit since it's built from natural rock. It's the remains of a monument erected on Bear Mtn, the highest mountain "summit" in Connecticut. The plaque reads that it was built by a mason in 1885 and states that it's the highest ground in the state of CT. The actual highpoint of ground was later determined to be on the south slope of nearby Mt. Frissell. The Appalachian Trail passes by this monument.