Contra Costa County— fire, flood & earthquake hazard information
Contra Costa County is a county in the San Francisco Bay Area, covering about 716.9 square miles. This page summarizes what official government maps show for Contra Costa County: CAL FIRE fire hazard severity zones, FEMA flood zones, state seismic hazard zones, dam inundation areas, airport noise contours, and air-quality indicators. Figures are the share of Contra Costa County’s area that falls inside each mapped zone.
View Contra Costa County on the interactive map → to check any specific address, free.
Wildfire hazard severity zones
Per CAL FIRE's Fire Hazard Severity Zone maps, 8% of Contra Costa County is in a Very High fire hazard severity zone, 25% is in a High zone, 9% is in a Moderate zone. The remainder of its area is outside currently designated zones.
| Very High severity zone | 8% |
| High severity zone | 25% |
| Moderate severity zone | 9% |
FEMA flood zones
16% of Contra Costa County lies within a FEMA Special Flood Hazard Area (1% annual chance, zones A/AE/AH/AO); less than 1% is in a coastal high hazard zone (V/VE); 2% is in the 0.2% annual chance (500-year) area. Federally backed mortgages in a Special Flood Hazard Area generally require flood insurance.
| Special Flood Hazard Area (100-yr) | 16% |
| Coastal high hazard (V/VE) | less than 1% |
| 0.2% annual chance (500-yr) | 2% |
Earthquake faults & seismic zones
The nearest mapped fault, the Concord fault, is about 0.5 mi (0.7 km) from the center of Contra Costa County. 17 named fault traces in the USGS Quaternary fault database cross its boundary. 32% of its area is in a state-designated liquefaction zone of required investigation. 19% is in an earthquake-induced landslide zone. 1% falls within an Alquist-Priolo earthquake fault zone, where new construction requires a fault study.
| Nearest mapped fault | Concord fault — 0.5 mi (0.7 km) |
| Named fault traces crossing boundary | 17 |
| Liquefaction zone | 32% |
| Earthquake-induced landslide zone | 19% |
| Alquist-Priolo fault zone | 1% |
Dam inundation, aircraft noise & air quality
13% of Contra Costa County lies within a state-reviewed dam-failure inundation area; annual average fine-particle (PM2.5) concentration across its census tracts is 8.6 μg/m³, and its composite pollution burden ranks around the 32th percentile statewide.
| Dam-failure inundation area | 13% |
| Annual PM2.5 (tract average) | 8.6 μg/m³ |
| Pollution burden percentile (statewide) | ~32 |
Frequently asked questions
- Is Contra Costa County in a wildfire hazard severity zone?
- Per CAL FIRE's Fire Hazard Severity Zone maps, 8% of Contra Costa County is in a Very High fire hazard severity zone, 25% is in a High zone, 9% is in a Moderate zone. The remainder of its area is outside currently designated zones.
- Is Contra Costa County in a FEMA flood zone?
- 16% of Contra Costa County lies within a FEMA Special Flood Hazard Area (1% annual chance, zones A/AE/AH/AO); less than 1% is in a coastal high hazard zone (V/VE); 2% is in the 0.2% annual chance (500-year) area. Federally backed mortgages in a Special Flood Hazard Area generally require flood insurance.
- What earthquake faults and seismic zones affect Contra Costa County?
- The nearest mapped fault, the Concord fault, is about 0.5 mi (0.7 km) from the center of Contra Costa County. 17 named fault traces in the USGS Quaternary fault database cross its boundary. 32% of its area is in a state-designated liquefaction zone of required investigation. 19% is in an earthquake-induced landslide zone. 1% falls within an Alquist-Priolo earthquake fault zone, where new construction requires a fault study.
- How do I check a specific address in Contra Costa County?
- Use the free sitelume interactive map at https://sitelume.com — search any Contra Costa County address to see which mapped zones it falls in, layer by layer.
Cities in Contra Costa County
Sources: CAL FIRE Fire Hazard Severity Zones; FEMA National Flood Hazard Layer; USGS Quaternary Faults; CGS Seismic Hazard Zones & Alquist-Priolo zones; Cal OES dam inundation maps; county ALUC noise contours; CalEnviroScreen 4.0. Area shares are computed against each place’s Census TIGER boundary (last computed 2026-07-24). Boundaries and zone designations change; always verify with the issuing agency.