Alto, CA— fire, flood & earthquake hazard information
Alto is a unincorporated community in Marin County in the San Francisco Bay Area, covering about 0.1 square miles. This page summarizes what official government maps show for Alto: 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 Alto’s area that falls inside each mapped zone.
View Alto on the interactive map → to check any specific address, free.
Wildfire hazard severity zones
CAL FIRE's current Fire Hazard Severity Zone maps do not designate any zones within Alto. Individual properties near the boundary can still fall inside a neighboring zone — check the exact address on the map.
FEMA flood zones
13% of Alto lies within a FEMA Special Flood Hazard Area (1% annual chance, zones A/AE/AH/AO). Federally backed mortgages in a Special Flood Hazard Area generally require flood insurance.
| Special Flood Hazard Area (100-yr) | 13% |
Earthquake faults & seismic zones
The nearest mapped fault, the San Andreas fault zone, is about 8.6 mi (13.9 km) from the center of Alto.
| Nearest mapped fault | San Andreas fault zone — 8.6 mi (13.9 km) |
Dam inundation, aircraft noise & air quality
annual average fine-particle (PM2.5) concentration across its census tracts is 8.6 μg/m³, and its composite pollution burden ranks around the 30th percentile statewide.
| Annual PM2.5 (tract average) | 8.6 μg/m³ |
| Pollution burden percentile (statewide) | ~30 |
Frequently asked questions
- Is Alto in a wildfire hazard severity zone?
- CAL FIRE's current Fire Hazard Severity Zone maps do not designate any zones within Alto. Individual properties near the boundary can still fall inside a neighboring zone — check the exact address on the map.
- Is Alto in a FEMA flood zone?
- 13% of Alto lies within a FEMA Special Flood Hazard Area (1% annual chance, zones A/AE/AH/AO). Federally backed mortgages in a Special Flood Hazard Area generally require flood insurance.
- What earthquake faults and seismic zones affect Alto?
- The nearest mapped fault, the San Andreas fault zone, is about 8.6 mi (13.9 km) from the center of Alto.
- How do I check a specific address in Alto?
- Use the free sitelume interactive map at https://sitelume.com — search any Alto address to see which mapped zones it falls in, layer by layer.
Nearby in Marin 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.