Stock photography, photos: acorn grinding hole Stock photos of Native Americans in California (Yokuts tribe, central California) would pound acorn nuts into flour on granite slabs, leaving these holes after years of use. In the central Sierra Nevada foothills near Fresno, CA, USA Photograph: © Len Wilcox Click for a larger image and more information Keywords associated with this stock photo: American,Indians,food,grain,grinding,rock,rocks,precolumbian,history,old,ancient,food preparation,west coast