Bedrock mortar

A bedrock mortar (BRM) is an anthropogenic circular depression in a rock outcrop or naturally occurring slab, used by people in the past for grinding of grain, acorns or other food products. There are often a cluster of a considerable number of such holes in proximity indicating that people gathered in groups to conduct food grinding in prehistoric cultures. Correspondingly the alternative name gossip stone is sometimes applied, indicating the social context of the food grinding activity. Typical dimensions of the circular indentations are approximately 12 centimeters in diameter by 10 centimeters deep, although a considerable range of depths of the cavities have been documented . The bedrock mortar has been identified in a number of world regions, but has been particularly intensely documented in the Americas. An alternative term for the bedrock mortar site is bedrock milling station.

A bedrock mortar should not be confused with a bedrock metate, which is a flat, trough-shaped depression often found with bedrock mortars.

Natufian bedrock mortars at Mount Carmel, Israel.

Maidu bedrock mortars in northern California.

Bedrock mortars at the Anza-Borrego Desert State Park in southern California.

Bedrock mortars used to grind acorns in California.

Hohokam bedrock mortars at Indian Kitchen, Arizona.

Bedrock mortars at Huerfano Butte.

A close up view of a bedrock metate at Huerfano Butte.

...
Wikipedia