On its age, its old homes and the National Register, Alto is more historic than 19% of U.S. towns. Its share of homes from before 1940 holds the grade up; its National Register listings pull it down.
C−
HistoryA character grade: shown, never part of Alto’s overall grade.
Few California towns list much on the Register (a typical California town has 0.0 per 10,000 residents, the U.S. 2.4), so Alto’s 0.0 sits below most of its state (31% of California towns have fewer) while its 0 listings outnumber those of 23% of U.S. towns.
How sure. Graded on two of the three inputs, so a change in either one moves the letter more than it would with three. The pre-1940 share is a Census survey estimate (±5.0 points).
Founding year: our sources. Homes: Census ACS 2020–24. National Register: National Park Service, May 2026 list; each listing counted once (boundary changes and added documentation belong to their listing), and a historic district counts its contributing buildings. How TownRatings grades history →
What stands out about Alto’s past
Read from the archive, the National Register and the record. The page puts what stands out first.
Wikipedia doesn’t have a history of Alto yet. The photos, dates and memories neighbors add here are how it gets written.
Alto (Spanish for "Tall") is a census-designated place adjacent to Mill Valley, California, United States, located in Marin County. It lies at an elevation of 26 feet (8 m). The population was 732 at the 2020 census.
Between the 2010 and 2020 censuses its population grew from 711 to 732 (+3%).
Intro from Wikipedia. Population: U.S. Census Bureau.
By decade
No old photos in the archives yet
Weddings on Main Street, storms, parades, school pictures, the old store. If it’s in your family album, it belongs here.
Be the first to add onePhotograph a print flat, in daylight, no flash.
Alto is more historic than 19% of U.S. towns. The History grade combines the town’s founding era, the share of homes built before 1940 and its National Register listings. It’s a character grade, so it isn’t part of the overall grade. How it works.
How old are the homes in Alto?
5% of Alto’s homes were built before 1940 (Census estimate, ±5.0 points), against a typical 3.4% for a California town; the median home was built in 1952.
Founding dates: Wikidata, Wikipedia, the U.S. post office records of Blevins & Helbock (CC0) and the Census. Homes by year built: Census ACS 2020–24. National Register of Historic Places: National Park Service (list of May 22, 2026). Old photos, postcards and papers: Wikimedia Commons, the Library of Congress and other public archives, credited on each item’s page. Maps: U.S. Geological Survey historical topographic maps (via Esri) and Sanborn fire-insurance maps (Library of Congress). History text and census tables: Wikipedia (CC BY-SA 4.0). Places that used to be: USGS Geographic Names Information System (2021).
