Natural hazards collage - natural hazard zones to considerWhat are the natural hazards in the San Francisco Bay Area and Silicon Valley?

The main natural hazards to consider are:

  • earthquakes
  • floods
    • 100 or 500 year flood plains
    • floods from dam failure or levee failure (includes rising sea and bay water levels)
  • liquefaction zones (and compressible soils areas)
  • landslide zones
  • fire risk areas, such as the Very High Fire Hazard Severity Zone
  • for those with basements (few homes), radon

There are zones associated with these potential risks and those areas are delineated by the state, county, and local jurisdictions. The state level earthquake faults are those which are considered active in relatively recent years. The county mapped fault zones may not have been active in over 10,000 years and the town or city labelled areas have been dormant for much longer than that.

Where to learn about natural hazards and natural hazard zones in Santa Clara or San Mateo Counties:

The Association of Bay Area Governments ( has a website full of relevant information.  One of their resources is a map displaying not just risk zones, but also quake risk based on which fault shakes. This same multi page PDF has info on flood risk (both flood plains and risk from dam failure), liquefaction, and even tsunami.

The flooding from dam failure map (page 53 of 56) is rare and, in my experience, hard to find for the county. The only other resource I’ve found for that is interactive and shows the risk for one dam at a time, and sometimes it’s glitchy and does not work great. If you want to avoid ALL of the areas prone to flooding in dam failure, you’ll appreciate this county level map, even if it’s not as clear as the interactive map.

You can find the interactive map here: the state of California’s Dam Breach Inundation Map Web Publisher.

Another excellent resource is the California OES My Hazards Awareness site. The fire zones are a little out of date, though.

For wildfire information, the best resource is Cal Fire’s map. You will need to zoom in quite a lot.

Other hazards which are both natural hazards and also environmental are naturally occurring asbestos (Communications Hill) and mercury (Almaden Valley).

Other hazards to consider are environmental, not natural hazards

There are other concerns, of course, to be aware of when relocating to or within Silicon Valley. The list could be nearly endless! Many of these are mapped and disclosed, but certainly not all.

Those including things such as the Superfund sites (primarily in Mountain View, Sunnyvale, Santa Clara, and parts of San Jose). These are disclosed on the natural hazard reports, or you can do a web search and find them.

Where we have mines or quarries, there’s dust which is unhealthy. Those areas are in Cupertino at the Lehigh or Permanente Quarry and also the Lexington Quarry on the backside of Blackberry Hill in Los Gatos near the Lexington Reservoir.

There are high transmission gas, power, and water lines that cross the valley. In some parts of Mountain View several of the gas lines run close to each other. PG&E has released maps showing the gas and electric lines, but Valley Water is not doing the same with the high transmission water lines. I’ve noticed that the high capacity water pipes often run under or near the high voltage power lines.

Something that does not make it onto the Natural Hazard Disclosure reports that we see in real estate transactions is the locations of crematoriums or crematories. Often they are on cemetery grounds or at the campus of a funeral home.  (Apparently a concern for human remains is mercury in fillings.)

There are no perfect areas or neighborhoods with zero risk as far as I can tell. My own home is out of the major areas, but is still in a 500 year flood plain (insurance not needed) and a Los Gatos town zone for some sort of fire risk, but I’ve not been able to see a map of that region or to learn if that’s the whole town or just the areas not in the Very High Fire Hazard Severity Zone.

What we advocate is familiarizing yourself with the various hazard zones in our area and then deciding what you’re most comfortable with.

Related reading

Smoke and air quality

Silicon Valley liquefaction zones (on, our Valley of Heart’s Delight blog)

Elevation map – learn your home’s elevation (on, our Valley of Heart’s Delight blog)

Do you  have a high water table? (on our Live in Los Gatos blog)

Are fire seasons new?