When we are out hiking on unfamiliar trails, especially in the mountains or on the Colorado Plateau, we watch for piles of rocks, called cairns, that indicate a trail. There is also a pastime that involves trying to make piles of rocks and balance them. This image is likely the later since there were no trails on this beach. In some National Parks, I have seen signs telling tourists not to disturb the cairns because they are historic trail markers. I don't think this pile qualifies.