Danger posed by earthquake fault will lead to some tighter building restrictions, including in La Jolla The state is creating new regulatory zones to protect people against the Rose Canyon fault. It will soon become harder to develop many properties in San Diego, including La Jolla, due to growing evidence that the Rose Canyon earthquake fault, which runs beneath the city, is larger and more active than scientists once thought. About 7,000 parcels in and around La Jolla, Old Town, San Diego International Airport and downtown San Diego will be placed in new regulatory fault zones. The California Geological Survey is creating the fault zones where developers of residential, commercial and public buildings may be required to show that their projects do not sit on top of active faults or are located a safe distance from such systems.