A fault-zone map starts a permit check, not a site verdict

Check the official map before you buy, divide, or design work on the land. If it is in an Alquist-Priolo Earthquake Fault Zone, call the city or county planning office. The zone is a rule area around a mapped active-fault trace. It does not show the fault’s exact place on one parcel.

Cities and counties must oversee covered projects in these zones. Before approval, they must require a geologic report on the surface-rupture hazard. There is a narrow waiver path. The local agency must find no undue hazard, and the State Geologist must approve the waiver.

Covered projects include land divisions and most structures built for people to occupy. Exclusions in state law can change what is required. A report approved in the past can also change the answer.

State criteria generally presume that active fault branches run under land within 50 feet of an active fault trace. An appropriate site investigation can show otherwise. This is not a universal 50-foot permit rule. The licensed-geologist report and local lead agency decide the site result. Local rules may be stricter.

Alquist-Priolo deals with surface fault rupture, not every earthquake risk. Other maps and rules cover shaking, liquefaction, landslides, and tsunami hazards.