Stone Structures
stacking rocks without mortar, including cairns, walls, platforms, open enclousre, roofed chambers and other shapes. Hoffman cataloged 5500 such stsructures across 16 states and 3 provinces, although mostly in New England, New York, and Pennsylvania. Need to date them, and find out. C14 is too iffy (the old carbon sneaking in, the direct association with a standing structure), and Feathers and his crowd used luminescence dating on 25 structures, using subsurface rocks or soils which have not been exposed since the structure was constructed.
Feathers, James K. and Shannon A. Mahan. "Luminescence Dating of Stone Structures in the Northeastern United States." American Antiquity, vol. 90, no. 1, 2025, pp. 174–90, Cambridge Core, doi:10.1017/aaq.2024.60.