The Hayward Fault is a major geological fault running roughly 51 miles through the eastern San Francisco Bay Area, from San Pablo Bay in the north to Fremont in the south. It sits directly beneath some of the most densely populated cities in California, making it one of the most dangerous faults in the United States.
Where the Fault Runs
The Hayward Fault cuts through the heart of the East Bay, passing beneath or near the cities of Richmond, El Cerrito, Berkeley, Oakland, San Leandro, Hayward, Union City, and Fremont. Its 51-mile trace (about 83 kilometers) follows the base of the East Bay hills, running northwest to southeast. Homes, schools, hospitals, highways, and critical infrastructure sit directly on top of it.
What makes the Hayward Fault especially concerning is not its size but its location. Unlike more remote faults, this one threads through neighborhoods where roughly 2.4 million people live and work today.
What Drives the Fault
The Hayward Fault is a strike-slip fault, meaning the ground on either side moves horizontally past each other rather than up and down. This motion is driven by the Pacific Plate grinding northwest past the North American Plate. The San Andreas Fault, California’s most famous fault, absorbs much of that plate boundary stress, but the Hayward Fault picks up a significant share of it along the East Bay.
The fault moves at an average rate of about 5 millimeters per year beneath the surface, roughly the speed your fingernails grow. Some of that movement happens as gradual, steady creep. Other sections remain locked, silently building up stress that will eventually release in an earthquake.
Creep You Can See With Your Eyes
One of the Hayward Fault’s most unusual features is that portions of it are constantly, visibly moving. Surface creep rates range from 3 to 9 millimeters per year along different segments. Over decades, this slow crawl cracks foundations, offsets curbs, and warps infrastructure built across the fault line.
The most famous example was at the intersection of Rose and Prospect streets in the city of Hayward, where the two sides of the street gradually pulled apart over the years. The offset curbs became a world-recognized symbol of a living, active fault. Even after repairs, the creeping ground begins pulling the new concrete apart again as soon as it cures. Similar creep damage shows up in roads, sidewalks, and building foundations throughout the East Bay.
Creep is not entirely bad news. Sections of the fault that creep are gradually releasing built-up stress, which may reduce the energy available for a sudden rupture. The problem is that creep doesn’t account for all the motion. Below about 4 to 6 kilometers deep, much of the fault is locked, and a particularly low-slip patch beneath San Leandro (moving less than 1 millimeter per year) suggests significant strain is accumulating there. That locked patch lines up with the source area of the fault’s last major earthquake.
The 1868 Earthquake
On October 21, 1868, the Hayward Fault produced an earthquake estimated at magnitude 6.8 to 7.0. At the time, the entire Bay Area had a population of about 260,000 people. Even so, the quake killed 30 people and caused extensive property damage across the region. It was one of the most destructive earthquakes in California history up to that point and earned the nickname “the Great San Francisco Earthquake” until the larger 1906 event on the San Andreas Fault took that title.
The 1868 rupture is believed to have broken the southern portion of the fault. More than 155 years have passed since then, and the locked sections of the fault have continued accumulating stress the entire time.
Connection to the Rodgers Creek Fault
For years, scientists debated whether the Hayward Fault connects to the Rodgers Creek Fault, which extends north of San Pablo Bay into Sonoma County. Detailed subsurface imaging has now confirmed that the two faults are directly linked at the surface. The Hayward Fault bends about 10 degrees to the right as it crosses San Pablo Bay before joining the Rodgers Creek Fault.
This connection matters enormously for earthquake risk. If both faults rupture simultaneously, the combined break could produce a magnitude 7.4 earthquake, significantly larger than the 1868 event. A USGS scenario modeling a 51-mile rupture of the Hayward Fault alone projects a magnitude 7.2 quake. A linked rupture with the Rodgers Creek Fault would extend the break even further, releasing more energy across a wider area and affecting communities on both sides of San Pablo Bay.
Why It Ranks Among the Most Dangerous U.S. Faults
The combination of factors is what makes the Hayward Fault stand out. It runs directly through a major metropolitan area. It has a documented history of producing damaging earthquakes. Large sections are locked and accumulating stress. And its physical connection to the Rodgers Creek Fault means a rupture could propagate across a longer distance than the Hayward Fault alone would suggest.
The Bay Area’s population is now roughly 30 times what it was in 1868, and the region’s infrastructure, from the BART transit tunnels that cross the fault to water and gas pipelines, sits in the direct path of any future rupture. A major Hayward Fault earthquake would affect not just the immediate East Bay but the broader regional and global economy, given the concentration of technology companies and port facilities in the area.