Indian Grinding Holes

Many centuries ago, Bay Miwok people who settled in this area used sandstone outcroppings to grind acorns and other seeds into meal, slowly forming cup-shaped depressions that served as mortar holes. Acorns from oak trees were a major food source for many California Indian groups. In autumn, baskets were filled with acorns, which were then dried, cracked, and shelled. Using bedrock mortars and rock pestles, the acorn was pounded into meal and then leached of its bitter tannic acid. This fine-grained meal was mixed with water and cooked into soup or mush by placing heated rocks into baskets.

California · United States