Alto, California
41 topographic sheets cover this place, the earliest surveyed in 1897 and the latest in 1995. It stands in the Southeast Marin census division. It lies in ZIP code area 94941. It stands on Ryan Creek. The Survey maps it on the San Rafael quadrangle. 732 people lived here at the 2020 count. It stands 26 feet above sea level.
Then and now
1897 to 1995The same ground, surveyed 98 years apart. Drag the handle to wipe between them. Both sheets are United States Geological Survey originals; neither has been altered.


Population over time
2 figuresAlto grew from 711 to 732 between 2010 and 2020. These are the recorded population figures Wikidata holds for this place, reached through the Geographic Names Information System number this page is keyed on rather than by name, so they belong to this place and not to another of the same name. Most are census counts, but not all are: an early figure may be a founding or settlement estimate, and an estimate published within five years of a census is left out. The change column is computed, and is left blank where more than 20 years separate a figure from the one before it, because a gap that long is not a change between two counts.
| Year | People | Change |
|---|---|---|
| 2010 | 711 | |
| 2020 | 732 | +21 (+3%) |
Topographic sheets covering this place
17 surveys from 41 printed sheetsMatched by testing this settlement's coordinate against the published boundary of every sheet in the United States Geological Survey's historical collection. Each opens the scanned sheet at the Survey.
- 1897 USGS Tamalpais quadrangle1:62500, 12 printings
- 1941 USGS Tamalpais quadrangle1:62500
- 1947 USGS San Francisco quadrangle1:250000
- 1948 USGS San Francisco quadrangle1:250000
- 1950 USGS Mt. Tamalpais quadrangle1:62500, 4 printings
- 1954 USGS San Rafael quadrangle1:24000, 7 printings
- 1955 USGS San Francisco quadrangle1:250000
- 1956 USGS San Francisco quadrangle1:250000, 4 printings
- 1957 USGS San Francisco quadrangle1:250000
- 1960 USGS San Francisco quadrangle1:250000
- 1961 USGS San Francisco quadrangle1:250000
- 1964 USGS San Francisco quadrangle1:250000
- 1971 USGS San Francisco quadrangle1:250000
- 1978 USGS San Francisco quadrangle1:100000, 2 printings
- 1985 USGS San Francisco quadrangle1:250000
- 1993 USGS San Rafael quadrangle1:24000
- 1995 USGS San Rafael quadrangle1:24000
Fires near this place
128 since 1992Regional context, not property-specific evidence. The federal wildfire occurrence database lists 128 fires within 5 miles of Alto between 1992 and 2020, burning about 158 acres in total. 1 started naturally. 6 were recorded as arson. Distance is straight-line from the map coordinates, so a fire counted here may appear on a neighbouring settlement's page as well.
| Reported cause | Fires |
|---|---|
| Missing data/not specified/undetermined | 78 |
| Equipment and vehicle use | 17 |
| Recreation and ceremony | 10 |
| Misuse of fire by a minor | 7 |
| Arson/incendiarism | 6 |
| Smoking | 4 |
| Power generation/transmission/distribution | 3 |
| Other causes | 1 |
| Debris and open burning | 1 |
| Natural | 1 |
The most recent of them, most recent first, with the day each was reported and the service that recorded it.
| Date | Cause | Size | Reported by | Name on the report |
|---|---|---|---|---|
| 8 September 2011 | Missing data/not specified/undetermined | under an acre | Marin County Fire Department | not named |
| 7 September 2011 | Missing data/not specified/undetermined | 3.0 acres | Marin County Fire Department | not named |
| 7 September 1992 | Recreation and ceremony | under an acre | Golden Gate National Recreation Area | LEACH |
| 5 September 2001 | Missing data/not specified/undetermined | under an acre | Golden Gate National Recreation Area | ALTA |
| 3 September 2020 | Missing data/not specified/undetermined | under an acre | Marin County Fire Department | not named |
| 3 September 2007 | Missing data/not specified/undetermined | under an acre | California Department of Forestry & Fire Protection | not named |
| 24 September 1993 | Power generation/transmission/distribution | 2.0 acres | Golden Gate National Recreation Area | TV#1 |
| 23 September 2010 | Missing data/not specified/undetermined | under an acre | California Department of Forestry & Fire Protection | not named |
Settlements close enough to share some of these fires:
Mines and quarries near this place
10 of 20 shownRegional context, not property-specific evidence. The federal mineral resources record lists 20 workings within 5 miles of Alto: 13 occurrences, 3 producers, 3 unknowns, 1 past producer. 3 still produce. What was taken out: Stone, Crushed/Broken, Manganese, Mercury, Silver. Distance is straight-line from the map coordinates, so a quarry counted here may appear on a neighbouring settlement's page as well.
| Where | Site | Commodity | Status | Recorded |
|---|---|---|---|---|
| Copperopolis Mine | Asbestos | Producer | Chrysotile | |
| Fort Baker | Gold, Manganese | Occurrence | 1914 | |
| Greenbrae | Sand and Gravel, Construction | Producer | ||
| Hotaling | Stone, Crushed/Broken, Stone, Dimension | Unknown | ||
| Tiburon Ridge Flagstone | Stone, Stone, Dimension | Occurrence | ||
| Claim | Mercury | Occurrence | ||
| Claim | Mercury | Occurrence | ||
| Escalle Quarry | Stone | Unknown | ||
| Hotaling | Stone | Occurrence | ||
| Mt Tamalpais | Silver | Occurrence |
Storms near this place
7 since 2010Regional context, not property-specific evidence. The National Weather Service names Alto in 7 storm reports between 2010 and 2024: 6 flood, 1 flash flood. No death or injury is recorded in these reports. Each account below is quoted exactly as the forecast office filed it, from the NOAA Storm Events Database, and each date opens the federal record of that event.
| When | Event | Place named | Harm | What the report says |
|---|---|---|---|---|
| January 2024 | Flood | Alto | $10 | The offramp from US Highway 101 North to California Route 1 North was closed due to flooding. |
| January 2023 | Flood | Alto | - | The underpass of California Highway 1 under US Highway 101 in Manzanita flooded. |
| January 2021 | Flood | Alto | - | Flooding on US-101 S and SR 1 off ramp. |
| February 2019 | Flood | Alto | - | SB 101 Seminary off ramp flooded. |
| December 2016 | Flash Flood | Alto | - | Roadway flooded on ramp at intersection of SR 131 and 101N. |
| December 2014 | Flood | Alto | - | Multiple lanes on Highway 101 blocked with flooding. |
| January 2010 | Flood | Alto | - | Heavy rain caused flooding on and around State Highway One in Marin City. On and off ramps and most lanes of the highway were closed. |
Nearest settlements
The eight closest, with where each one stands in the county. Distances are straight-line, computed from the Geographic Names Information System coordinates.
| Map | Place | Distance | Sheets |
|---|---|---|---|
| Homestead Valley | 0.7 miles | 41 | |
| Strawberry Manor | 1.0 miles | 41 | |
| Almonte | 1.0 miles | 41 | |
| Strawberry | 1.0 miles | 41 | |
| Mill Valley | 1.0 miles | 41 | |
| Chapman | 1.1 miles | 41 | |
| Reed | 1.3 miles | 41 | |
| Bel Aire | 1.4 miles | 39 |
Elsewhere
Matched on this settlement's Geographic Names Information System number rather than its name, so it cannot be a different place of the same name in another state.
| Wikipedia article on Alto | An encyclopaedic summary. Its text is share-alike, so it is linked here rather than copied. |
| Wikidata item Q4736768 | The structured record the population and elevation above come from. Public domain (CC0). |
Provenance
This settlement is recorded in the Geographic Names Information System as feature 218191. The sheet list is computed by point-in-boundary test against the United States Geological Survey's historical topographic inventory. Both are works of the United States government and carry no copyright under 17 U.S.C. 105.
Wildfire. Short, Karen C. 2022. Spatial wildfire occurrence data for the United States, 1992-2020 [FPA_FOD_20221014]. 6th Edition. Fort Collins, CO: Forest Service Research Data Archive. https://doi.org/10.2737/RDS-2013-0009.6 Collected with United States Government funding and usable without additional permissions or fees.
Mines and quarries. USGS Mineral Resources Data System (MRDS) https://mrdata.usgs.gov/mrds/ A work of the United States government, no copyright under 17 U.S.C. 105.
Storms. NOAA National Centers for Environmental Information, Storm Events Database https://www.ncei.noaa.gov/stormevents/ A work of the United States government, no copyright under 17 U.S.C. 105. Narratives are quoted verbatim from the National Weather Service report and are not edited or summarised.
















