MYSTERY WALLS OF THE EAST BAY: Mission Peak Regional Preserve Part I History On the east side of San Francisco Bay, thousands of people travel on Highway 680 between Milpitas and Fremont. Stuck in traffic, a few might notice a dark streak high on a ridge, and assume it’s just another outcrop in a rocky hillside. It’s not. It’s one fragment in the Great Mystery of the Bay Area--the Walls on the Mountains. No one knows who built them, or why. They follow no obvious pattern an