September 28, 2006
The boundary between the North American Plate and the Pacific Plate is a complex region of intertwining faults that follow the granddaddy of them all, the San Andreas Fault. One of the major splinters is the Calaveras Fault. It runs through Hollister, California and is most evident in the vicinity of Dunne Park. Unlike the San Andreas Fault, which is usually “locked” for many years until it shifts and causes an earthquake, the Calaveras Fault is creeping steadily along at about half an inch per year. As a result, roads and houses built on the fault are slowly being sheared and shifted, and must be patched frequently. When it is not feasible to repair them, the damage accumulates year by year.
In the vicinity of Dunne Park, the fault is obvious as offset curbs and sidewalks for many blocks north and south of the Park. A low scarp roughly two feet high runs through barbecue area on the east side of the park. In this photograph, the built-up motion is revealed as a prominent 2 ft (.65 m) side step in the sidewalk where the fault crosses from right to left. This means that the last time they paved the sidewalk was about 50 years ago. Offsets in the curbs are much smaller, the result of more recent paving and straightening of the road. How would you like to be a real estate agent in Hollister? Photo taken n May of 2004.