Trace of Hayward Fault Union City to South Fremont

The Hayward Fault is an offset of the San Andreas Fault system that dominates the landforms of eastern San Francisco Bay.  The relative motion between the North American Plate  (southeast) and the Pacific Plate  (northwest) create stress that releases energy as earthquakes. This slip slide motion is called a transform fault.  The Hayward Fault is within the San Andreas Fault  Boundary Zone between the North American Plate and the Pacific Plate.  The Hayward fault is one of only a few dozen faults in the world that “creeps,” or slowly moves.  Evidence of creep can be found from Pt. Pinole in the north to south Fremont.

In the Fremont area the Hayward Fault dissects the city.  It goes through the flat land starting in Warm Springs and goes back into the hills around the Niles/Union City area. This allows for urban features such as offset curbs, compression knoll, depressions, cracks, and more.  Pull apart features also causes elongated water features such as Tule Ponds at Tyson Lagoon and the historic Stivers Lagoon.

Field Guide from Tule Ponds at Tyson Lagoon to Stivers Lagoon (pdf)(2006)