Most of Diablo was built recently: 0.0% of its homes predate 1940 and the median home dates from 1980. Below: maps from 1896 on and the census since 2000.
Founding year: the first Diablo post office (Blevins & Helbock, CC0).
History grade
What drives Diablo’s History grade
On its age, its old homes and the National Register, Diablo is more historic than 3% of U.S. towns. Its National Register listings hold the grade up; its share of homes from before 1940 pulls it down.
D−
HistoryA character grade: shown, never part of Diablo’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 Diablo’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 any two of the three inputs instead, the letter would range from D− to D. The pre-1940 share (±2.9 points) is firm at this size. The founding year is the first post office, not a stated founding date.
Founding year: the first post office (other dates in Quick answers). 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 Diablo’s past
Read from the archive, the National Register and the record. The page puts what stands out first.
Every edition of the U.S. Geological Survey’s map of Diablo. Tap a year, or press play to watch the town change.
1896Mt Diablo sheet · 1:62,500
U.S. Geological Survey historical topographic maps (public domain), via Esri’s collection of the scans. The red ring marks the center of Diablo.
The story so far
Diablo, in brief
Wikipedia doesn’t have a history of Diablo yet. The photos, dates and memories neighbors add here are how it gets written.
Diablo (Spanish for "Devil") is a census-designated place (CDP) in Contra Costa County, California, United States. The population was 1,255 at the 2020 census. It is located 2.5 miles (4.0 km) east-northeast of Danville.
Its first post office opened in 1916. Between the 2010 and 2020 censuses its population grew from 1,158 to 1,255 (+8%).
Intro from Wikipedia. Population: U.S. Census Bureau.
From the old history books
What they wrote about Diablo, 1882–1926
Passages that mention Diablo, cut from the printed page as they were published.
History of Contra Costa County, California1926 · page 171Read the page →
Read the text
CLAYTON The village of Clayton, located at the base of Mount Diablo, at the head of Diablo Valley, was named after Joel Clayton and was started in 1857, when he laid out one street and platted a few lots on either side. The prospecting for coal was the primary reason of founding a settlement. W. K. Taylor surveyed the site in 1858. The first house erected on the present site of the town was built in 1857 by Romero Mauvais, who erected a building and opened a tavern. This latter became the site
Text read by machine from the scan; it may contain errors.
History of Contra Costa County, California, including its geography, geology, topography, climatography and description1882 · page 40Read the page →
Read the text
Diablo, Ygnacio, and Walnut Creek Valleys. Other smaller but important and beautiful little serpentine valleys coil up and almost surround the mountain, till lost in the narrowness of their waterways. The most important of these small valleys is San Kanion, extending from Walnut Creek Valley south, to the Alameda county line, quite dividing the main range of mountains from its Diablo spur, making a natural and easy highway through the county and around the peak of Diablo. In places this valley is as narrow as half a mile, while at others it spreads to one and a half miles,
Text read by machine from the scan; it may contain errors.
History of Contra Costa County, California, including its geography, geology, topography, climatography and description1882 · page 469Read the page →
Read the text
CLAYTON.— The little village of Clayton lies snugly nestled at the foot of Mount Diablo, on its northern side, and at the head of Mount Diablo valley, which extends from the town of Pacheco, in a southeasterly direction, to the foot of the mountain, a distance of some eight or nine miles The place takes its name from Joel Clayton, whose son is still a resident of the neighborhood, and was started in 1857, Mr. Clayton only laying out one street, and a few lots on either side of it. His object in establishing a village at all, was the prospect of finding coal in the vicinity. He had been,
Text read by machine from the scan; it may contain errors.
History of Contra Costa County, California1926 · page 364Read the page →
Read the text
October 7, 1925. — The harvesting of over eighty tons of cucumber seed in Diablo Valley started Tuesday. Three hundred and fifty acres of cucumbers have been planted in Diablo Valley, being grown exclusively for seed. These are grown as an intercrop in the young orchards and, with 350 acres planted producing better than 500 pounds of seed per acre, will bring in a revenue of crop close to fifty thousand dollars.
Text read by machine from the scan; it may contain errors.
Scans and text from the Internet Archive. Books published in 1930 or earlier, which are in the public domain.
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.
The Diablo post office opened in 1916, the earliest record of the town by name (U.S. post office records).
How does Diablo rank for history?
Diablo is more historic than 3% 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 Diablo?
0.0% of Diablo’s homes were built before 1940 (Census estimate, ±2.9 points), against a typical 3.4% for a California town; the median home was built in 1980.
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).
From U.S. Geological Survey historical maps, U.S. Census counts (via Wikipedia), the US Post Offices dataset (Blevins & Helbock), the USGS Geographic Names Information System and old county and town histories (Internet Archive). Archive images are copied here with their credits and licenses, shown on each photo’s page. Refreshed monthly.
