East Bay Walls, Ancient stone walls in San Francisco Bay Area, California.

East Bay Walls are stone structures found throughout the East Bay region that were built without mortar using locally gathered materials. They vary widely in length and in the size of stones used, ranging from small rocks to massive boulders.

No written record identifies who built the walls or when. Lichen testing suggests construction between 1850 and 1880, in the early American era, possibly by European settlers using Chinese, Mexican or Native American labour; their extent and the manpower needed have also led some to attribute them to the Ohlone.

No written record names the builders. Lichen testing points to construction between 1850 and 1880, and settlers may have used Chinese, Mexican or Native American labour; some researchers suggest the Ohlone built them earlier. Visitors can still find stretches sunk into the soil and overgrown with grass.

The walls can be seen at several accessible locations, including Ed R. Levin County Park and Mission Peak Regional Preserve. The best way to explore them is by hiking through the hills where they appear at many points along the routes.

The name "Berkeley Mystery Walls" is a misnomer: similar walls occur throughout the hills around San Francisco Bay and as far as Chico, Red Bluff and Montague. As of 2016, archaeologist Jeffrey Fentress was measuring and mapping them to seek protection from development. Many formations have sunk into the earth and are often overgrown.