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Alto, CA
Full City Profile · California · San Mateo County County
3.0
/5.0
B
Good
866
Population
6,662/sq mi density
$2,000,001
Home Value
$2,016,416 Zillow
59°F
Avg Temperature
305 sunny days/yr
76
Violent Crime/100K
1,305 property/100K
B
Overall
3.0 / 5.0
Good overall score based on economy, affordability, safety and education
F
Safety
1.0 / 5.0
76 violent crimes/100K
A+
Education
5.0 / 5.0
66.4% bachelor's degree or higher
Alto enjoys a temperate climate with an average annual temperature of 59°F (15°C). Winters average 49°F in January while summers reach 68°F in July. The area gets 305 sunny days per year. Annual precipitation totals 44.4 inches. The area receives 0.0 inches of snow annually. Air quality is rated Good with a median AQI of 48.
Temperature
49°F Jan (10°C)
68°F Jul (20°C)
| Annual Average | 59.3°F |
| 10% above US avg | |
| January Average | 49°F (10°C) |
| July Average | 68°F (20°C) |
| Sunny Days | 305 days/yr |
Geography
| Elevation | 19 ft (6 m) |
| Area | 0.1 sq mi (0.3 km²) |
| Population Density | 6,662/sq mi |
| Coordinates | 37.9056°N, 122.5187°W |
| Timezone | America/Los_Angeles |
| County | San Mateo County County |
| Nearest Airport | Metro Oakland International (OAK) 21 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 48.0 |
| Rating | Good |
Air Pollutants (EPA 2023)
| Ozone (O₃) | 0.0332 ppm |
| NO₂ (Nitrogen Dioxide) | 12.1 ppb |
| CO (Carbon Monoxide) | 0.34 ppm |
| PM2.5 (Fine Particles) | 4.5 μg/m³ |
Natural Hazard Risk
| Overall Risk | Relatively High |
| Risk Score | 99.2 / 100 |
| Social Vulnerability | 20.5 / 100 |
| Community Resilience | 97.6 / 100 |
Hazard Breakdown
| Tornado | Relatively Low |
| Earthquake | Relatively High |
| Wildfire | Relatively Moderate |
| Flood | Relatively High |
| Hail | Very Low |
| Strong Wind | Relatively Low |
| Heat Wave | Relatively Moderate |
| Winter Weather | Very Low |
| Lightning | Relatively Moderate |
| Drought | Relatively High |
| Cold Wave | No Rating |
| Landslide | Relatively High |
| Coastal Flood | Relatively High |
| Tsunami | Relatively Moderate |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Tsunami History
5 tsunamis recorded within 500 km. Highest wave on record: 4.5 m (15 ft).
| Year | Location | Cause | Max Wave | Deaths | Distance |
| 1868 | N. CALIFORNIA | Eruption + Earthquake | 4.5 m | 30 | 43 km |
| 1989 | N. CALIFORNIA | Earthquake | 1.0 m | 62 | 112 km |
| 1856 | N. CALIFORNIA | Eruption + Earthquake | 0.6 m | — | 49 km |
| 1906 | N. CALIFORNIA | Eruption + Earthquake | 0.1 m | — | 23 km |
| 1865 | N. CALIFORNIA | Eruption + Earthquake | — | — | 96 km |
Source: NOAA/NCEI Historical Tsunami Database. Sorted by wave height.
Nearby Volcanoes
1 volcano within 200 km. Closest: Clear Lake (120 km).
| Name | Type | Elevation | Last Eruption | Distance |
| Clear Lake | Volcanic field | 1,439 m (4,721 ft) | Unknown | 120 km |
Source: Smithsonian Institution Global Volcanism Program (GVP). Sorted by distance.
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 49°F (10°C) | 9.0 in | Wettest |
| February | 51°F (11°C) | 7.5 in | |
| March | 53°F (11°C) | 6.3 in | |
| April | 55°F (13°C) | 2.6 in | |
| May | 58°F (15°C) | 0.8 in | |
| June | 62°F (16°C) | 0.2 in | |
| July | 68°F (20°C) | 0.1 in | Warmest, Driest |
| August | 65°F (18°C) | 0.2 in | |
| September | 65°F (18°C) | 0.4 in | |
| October | 62°F (16°C) | 2.2 in | |
| November | 54°F (12°C) | 6.3 in | |
| December | 49°F (10°C) | 7.6 in | Coldest |
Alto has a seasonal temperature swing of 19°F / from 49°F in December to 68°F in July. Total annual precipitation is 43.3 inches, with January being the wettest month (9.0") and July the driest (0.1").