The Hayward Fault Zone is a right-lateral strike-slip geologic fault zone capable of generating destructive earthquakes. The fault was first named in the Lawson Report of the 1906 San Francisco Earthquake in recognition of its involvement in the earthquake of 1868. This fault is about 119 km (74 mi) long, situated mainly along the western base of the hills on the east side of San Francisco Bay. It runs through densely populated areas, including Richmond, El Cerrito, Berkeley, Oakland, San Leandro, Castro Valley, Hayward, Union City, Fremont, and San Jose.
Preferential groundwater flow along the fault emerges as a spring supporting the riparian vegetation in the center of this photo of Taylor Mountain Regional Park. The spring is the source of Cooper Creek which flows northward through a deeply incised canyon along the fault on the southern edge of Santa Rosa, California, to a confluence with Matanzas Creek at Doyle Community Park.