The East Bay hills are beautiful, and much of them are moving. Not dramatically — fractions of an inch per year in most places — but persistently, in mapped, named, well-documented slow-moving landslides that have been cracking foundations and shifting streets for as long as the hills have been built on. Here is the geology behind it, exactly where to check whether a property is in a mapped zone, and what surveys and investigations California law requires when it is.
Why the East Bay Hills Creep
The hills are built largely of weak sedimentary and volcanic rock: the Orinda Formation (poorly cemented siltstones and claystones), the Moraga Formation volcanics, and sheared Franciscan mélange. On steep slopes these materials host deep-seated earthflows — landslides whose slide surface sits well below the ground, moving the entire hillside above it.
Most of the time, movement is creep: millimeters to a few inches per year. In wet winters — 2017 and the 2023 atmospheric-river season are recent examples — groundwater rises, and dormant slides reactivate or accelerate. The signature isn't a dramatic collapse; it's doors that stop closing, stair-stepped cracks in stucco, tilted retaining walls, fences drifting out of line, and pavement cracks that get patched and return.
- Blakemont area (Kensington / El Cerrito border) — a documented slow-moving landslide area that has damaged homes and streets for decades.
- Berkeley and Oakland Hills — the flanks of Grizzly Peak, Claremont Canyon, and parts of Montclair include mapped dormant and active slides; many pre-1970s subdivisions were built before modern grading codes.
- Orinda, Moraga, Lafayette — the Orinda Formation's home turf; hillside repairs on cut-slope lots are a recurring theme.
And Then There's the Hayward Fault
Separate from landslides but woven through the same hills: the Hayward fault runs the length of the East Bay through Fremont, Hayward, San Leandro, Oakland, Berkeley, and El Cerrito. Uniquely among major faults, it creeps aseismically at roughly 5 millimeters per year — you can see offset curbs and sidewalks in Hayward and Fremont, and the creep famously split UC Berkeley's Memorial Stadium, which straddles the trace. Creep quietly relocates fences, walls, curbs — and survey monuments — a little more every year.
Check Your Property: Free Official Maps
- CGS EQ Zapp — the California Geological Survey's official address-searchable map of Alquist-Priolo earthquake fault zones and seismic hazard zones (earthquake-induced landslide and liquefaction): maps.conservation.ca.gov/cgs/EQZApp. This is the map that determines the legal requirements below — start here.
- USGS Bay Area landslide inventories — USGS has mapped historic and dormant landslide deposits across the Bay Area; search "USGS San Francisco Bay region landslides" for the published maps and data.
- County GIS — Alameda County's parcel viewer and Contra Costa County's GIS portal overlay hazard layers on individual parcels.
- City hillside overlays — Oakland's S-11 overlay and Berkeley's Hillside Overlay flag areas with additional development review; your city's zoning map shows whether they apply.
What the Law Requires If You're in a Zone
- Alquist-Priolo Earthquake Fault Zoning Act — in a mapped fault zone, a geologic investigation is required before building structures for human occupancy, no structure may be placed across an active fault trace, and a setback (50 feet by default) applies. Hayward-fault AP zones cross much of the East Bay hills' lower flanks.
- Seismic Hazards Mapping Act — in a mapped "zone of required investigation" for earthquake-induced landslide or liquefaction, most development permits require a site-specific geotechnical investigation addressing the hazard, reviewed by the permitting agency.
- Natural Hazard Disclosure — every California home sale must disclose whether the property sits in these mapped zones. Buyers in the hills should read this section of the NHD report, not skim it.
Where the Land Surveyor Comes In
- Topographic base mapping. Every geotechnical investigation and hillside permit set is built on a surveyed topographic base. Our laser-scanned topo captures the full slope — walls, cracks, scarps, drainage — in one visit. See topographic surveys.
- Deformation monitoring. If a slope is suspected of moving, the question is where and how fast. We scan the slope as a baseline, re-scan at intervals, and difference the point clouds — millimeter-level change detection across the entire hillside, not just a few stakes. The record supports geotechnical design, repairs, insurance, and disclosure. See deformation monitoring.
- Boundary and monument work on moving ground. Creep drags fences, walls, and survey monuments with it — over decades, occupation lines and deed lines diverge. Boundary retracement in creep zones leans on monument evidence and record research, and monuments in construction zones get preserved per §8771. See monument preservation.
Buying, Building, or Watching Cracks Widen?
Five minutes on EQ Zapp tells you whether a property is in a mapped zone. If it is — or if the doors and stucco are already telling you something is moving — a scan-based baseline is the cheapest insurance there is: it turns "I think it's moving" into measured fact. We're happy to talk through what your site needs.