Workers digging the new fourth bore of the Caldecott Tunnel are getting a once-in-a-lifetime view of one of the defining features of the East Bay: the range of hills that runs from San Pablo Bay south to Fremont. By visiting just a few accessible sites aboveground, you can find clues that tell the story of how these hills rose from their humble origins as deep ocean sediments and volcanic flows to the iconic fault-riddled hillsides of today.
It was 140 years ago, in October 1868, that the Hayward Fault unleashed the magnitude 6.8 temblor that put the fault on the map. The quake shook the entire region and virtually leveled the then-small hamlets of Hayward and San Leandro. Now, the land along the fault line is among the most densely populated in the region, a sobering situation given the likelihood of a repeat performance in the near future. But despite their destructive potential, the Hayward and the Bay Area’s other faults are the driving force behind our region’s varied and beautiful topography. Understanding how they work is key both to understanding our local landscapes and to preparing for the next Big One.
The peaceful hills of Black Diamond Mines Regional Preserve weren’t always so: One hundred twenty years ago, you’d have found bustling towns full of miners and their families and, nearby, the mine works and railroads that carried out tons of coal and sand, feeding the booming industries of Northern California. Today, the park offers grand vistas, abundant wildflowers, and a mine tour that gives an illuminating view of both the work of the miners and the geological history that brought them here and shaped the aboveground landscape.
Perched 600 feet above San Francisco Bay, Ring Mountain has spectacular views of the surrounding ridgelines, Bay, and urban areas. But you can also find much deeper views into the earth preserved in the remarkable rocks strewn about this wild and open landscape.
On April 18, 1906, a massive earthquake centered just west of San Francisco ruptured the earth from Humboldt to San Juan Bautista. While the more dramatic traces of this 7.8 temblor may be hard to find one hundred years later, the tectonic forces that moved the earth that day are still relentlessly shaping our young and active landscape, carrying us towards another cataclysm in the near future.