Unexplained Rock Features in Southwestern Arizona

Human-laid configurations of native rock are common archaeological features in southwestern Arizona, but we have observed six large rock features that do not readily fit into the current categories or explanations of purpose. Our features are distributed across a large area and as far as 150 km apart. All are exceptionally large piles of cobble-sized rocks placed perpendicularly across foot trails, in four cases lying along the crest of a pass, one on a mesa, and one at the mouth of a canyon. Taken as units, they rank among the most massive rock features in the region and are not yet explained. In this paper, we describe these enigmatic features and offer suggestions as to their builders, age, and purpose.