This rock art panel painted on granite sits in a shallow canyon along the foothills of a mountain range on the edge of California’s Mojave Desert. More art adorns the underside of a natural shelter formed by the boulders, but has been nearly entirely erased by the elements. A large millstone with numerous mortars lays at the foot of the painted rock and an adjacent boulder is also painted.
I always marvel at deep mortars bored into granite, an exceedingly hard stone. It reflects many long hours of use. Note the patina surrounding the work surface of the stone compared to the rougher edges of the boulder, which also reflects long use of the site. How long might it take to polish granite like that from mere contact with the hands, feet and rumps of humans using the mortars?