Building in a
landslide zone.

The legal basis

California's Seismic Hazards Mapping Act directs the state geologist to identify and map areas prone to earthquake-induced landslides, designating them as Zones of Required Investigation. Cities and counties are required by this state law to mandate a site-specific investigation before issuing a development permit or approving a subdivision within one of these zones — it's not a local discretionary policy.

What the investigation actually has to determine

The report has to determine whether a significant hazard actually exists at your specific site and, if one does, recommend measures to reduce the risk to an acceptable level. This is a real hazard evaluation, not a formality — it has to define and delineate the actual seismic hazard affecting your parcel.

Who's qualified to do it

The investigation has to be performed by a state-licensed engineering geologist and/or civil engineer — not a general contractor, and not a standard soils testing firm without that specific licensure.

How this differs from a standard hillside soils report

A landslide zone investigation is narrower and more specific than the general geotechnical report that can apply to hillside new construction — it's evaluating a mapped, state-designated seismic hazard specifically, with mitigation measures tied directly to that hazard, not a general site-suitability review.

How to find out if you're in one

The California Geological Survey publishes the official Seismic Hazard Zone maps, which show whether a specific parcel falls inside a mapped Zone of Required Investigation for landslides. This is a checkable fact about your property, not a guess based on visible slope.

What this means for your project

If your lot is in a mapped zone, this report is a required step in the permit process, not an optional upgrade — it needs to be budgeted and scheduled from the start. We confirm your property's actual zone status early, since finding out mid-permit costs real time on top of the report itself.