Altadena () is an unincorporated areaLos Angeles County publication: "Unincorporated Areas within the County of Los Angeles", Altadena listed by Los Angeles County government office, as an unincorporated city , "Los Angeles County publication: 'Unincorporated Areas within the County of Los Angeles'", verified September 27, 2010Los Angeles County Office of Unincorporated Area Services, Altadena listed by Los Angeles County government office, as an unincorporated area , "Los Angeles County Office of Unincorporated Area Services", verified September 27, 2010 and census-designated place in the San Gabriel Valley and the Verdugos regions of Los Angeles County, California. Directly north of Pasadena, it is located approximately from Downtown Los Angeles. Its population was 42,846 at the 2020 census, up slightly from a 2010 figure of 42,777. In early 2025, the community was severely impacted by the Eaton Fire.

History Etymology The name Altadena was coined by Byron O. Clark, who established Altadena Nursery in 1875. The name combines the Spanish alta, meaning "upper", with dena, a term he adapted from Pasadena. The area is adjacent to, but at a higher elevation than, Pasadena.

Early history In the mid-1860s, Benjamin S. Eaton first developed water sources from the Arroyo Seco and Eaton Canyon to irrigate his vineyard near the edge of Eaton Canyon. This made possible the development of Altadena, Pasadena, and South Pasadena. He did the construction for B. D. Wilson and Dr. John Griffin, who jointly owned the Mexican land grant of Rancho San Pascual, about , that would be the future sites of those three communities. They hoped to develop and sell the land in a real estate plan called the San Pasqual Plantation. Their efforts failed by 1870, despite Eaton's irrigation ditch that drew water from the site of present-day Jet Propulsion Laboratory (JPL) in the Arroyo Seco, because the land was relatively inaccessible and few believed crops could thrive that close to the mountains.

Eaton tried to sell the land for the partners, and in late 1873, he helped broker a deal with Daniel Berry, who represented a group of investors from Indiana, to buy of the rancho. That included the land of present-day Altadena, but they developed a section farther south as Pasadena.

Byron O. Clark established a nursery in the foothills in 1875, which he named "Altadena Nursery", a name he coined from the Spanish alta meaning "upper" and dena from Pasadena.

In 1880 or 1881, Capt. Frederick Woodbury, and his brother, John Woodbury of Marshalltown, Iowa, purchased known as the Woodbury Ranch. The land remained primarily agricultural, although several Eastern millionaires built mansions along Mariposa Street, and a small community developed through the 1890s and into the next century.

Development

John Woodbury established the Pasadena Improvement Company in 1887, with a plot plan of residential development referred to as the Woodbury Subdivision. They contacted Byron O. Clark, who had moved away, and asked if he could use the name "Altadena" for his subdivision; Clark agreed.

The newly sprouted community of Altadena immediately began to attract millionaires from the East. In 1887 Andrew McNally, the printing magnate from Chicago, and his friend, George Gill Green, had built mansions on what was to become Millionaire's Row: Mariposa Street near Santa Rosa Avenue. Newspaper moguls William Armiger Scripps and William Kellogg built homes side by side just east of Fair Oaks Avenue. A bit farther east, Zane Grey bought a home from Arthur Herbert Woodward, and added a second-floor study. The famous Benziger Publishing Company built a mansion on the corner of Santa Rosa Avenue (Christmas Tree Lane) and Mariposa. Mariposa was taken from the Spanish name for a butterfly. The grandson of Andrew McNally, Wallace Neff, became a famous Southern California architect. He started his career in Altadena with the design and construction of St. Elizabeth of Hungary Catholic Church (parish est. 1918), which was dedicated in October 1926.

From 1924 to 1926, 160 homes were built in Altadena by the fugitive conman Elisha Paul Janes, with distinctive steep roofs and multiple gables; despite his lack of qualifications, they proved popular, and the neighborhood was designated as a heritage area in 2002.

Many notable buildings followed in the 1930s, including Eliot Junior High School (1931) and Davies Community Center in Farnsworth Park (1934).

Later history Redlining policies prevented African Americans from acquiring land or purchasing property in much of California. One of the areas exempt from these policies was Altadena Meadows, which thrived and became one of the first middle-class African American neighborhoods in the area.

While Altadena long refused wholesale annexation by neighboring Pasadena, the larger community nibbled at its edges in several small annexations of neighborhoods through the 1940s. Attempted annexation was stopped in 1956 by community campaigns though it has been resurrected several times since by Pasadena without success. Had the annexation succeeded, Pasadena would be the 108th largest city in the United States.

With early-1960s redevelopment in Pasadena, the routing of extensions of the 134 and 210 freeways, and lawsuits over the desegregation of Pasadena Unified School District, there was white flight and convulsive racial change in Altadena. In 1960, its black population was under four percent; over the next 15 years, half the White population left, and was replaced by people of color, many of whom settled on the west side of town after being displaced by Pasadena's redevelopment and freeway projects.

In 1993, the Kinneloa Fire, begun accidentally on the slopes above Eaton Canyon, burned dozens of homes in Altadena and neighboring Kinneloa Mesa as part of a rash of late October wildfires driven by Santa Ana winds in Southern California. One man died of complications from smoke inhalation and dozens were injured.

In 2022, Altadena gained local coverage in Los Angeles as the place of the first land return to the Tongva since the arrival of Europeans in the Los Angeles Basin area, after a resident donated her 1-acre property to the Tongva Taraxat Paxaavxa Conservancy. It was described as marking the first time in nearly 200 years that the Tongva have had land in Los Angeles County.

In 2022, a single lottery ticket was sold to Edwin Castro, which would win a world record US$2.04 billion Powerball jackpot, announced on November 7, 2022. After a few months of paperwork, on February 14, 2023, Castro publicly accepted the lump sum prize of US$997.6 million.

Eaton Fire (2025)

On January 7, 2025, the Eaton Fire started in Altadena around 6:30 PM local time (PT) during powerful Santa Ana Winds. It quickly spread to by January 10, with 19 confirmed fatalities.

Over 9,000 structures were damaged or destroyed, including the Andrew McNally House, Altadena Community Church, St. Mark's Episcopal Church, The Bunny Museum, and Scripps Hall, as well as much of the downtown area. The entirety of Altadena was put under an evacuation order.

In the aftermath of the fires, many homeowners struggled with high rebuilding costs, and some were forced to sell. Luxury developers and wealthy individuals scrambled to buy lots in cash at competitive prices. Community groups such as Altadena Not for Sale were quickly formed to advocate for the underinsured and uninsured to protect against land speculators.

Following the January 2025 Eaton Fire in Altadena, Powerball jackpot winner Edwin Castro began purchasing several fire-damaged lots in his hometown. Through his company, Castro announced plans to use a portion of his winnings to construct single-family homes for local residents while preserving the community’s architectural character and preventing speculative real-estate development. Castro's involvement in the rebuilding process has been met with both praise and concern from residents, who cite hopes for community recovery alongside worries about affordability and land consolidation.

Geography For statistical purposes, the United States Census Bureau has defined Altadena as a census-designated place (CDP). According to the United States Census Bureau, the CDP has a total area of , over 99% of it land.

Climate Altadena experiences hot and dry summers that are followed by warm and windy falls and mild winters. According to the Köppen climate classification system, Altadena has a hot-summer Mediterranean climate, abbreviated Csa on climate maps.

The wettest calendar year was 1983, with , and the driest was 1947, with . The most rainfall in one month was , in February 1980. The most rainfall in 24 hours was , on March 2, 1938. Altadena averages of rain a year, over more than nearby Los Angeles due to the orographic effect created by the San Gabriel Mountains. Because of the slope on which the city is built, sewer lines in the city's northern section have been known to overflow significantly.

Demographics

Altadena first appeared as an unincorporated community in the 1960 U.S. census; and as a census-designated place in the 1980 United States census.

Racial and ethnic composition

+Altadena CDP, California – Racial and ethnic compositionRace / Ethnicity (NH = Non-Hispanic)Pop 1980Pop 1990Pop 2000Pop 2010Pop 2020% 1980% 1990% 2000% 2010% 2020White alone (NH)18,23718,49416,84817,23117,90045.02%43.35%39.54%40.28%41.78%Black or African American alone (NH)17,15916,12413,1129,8167,13642.36%37.80%30.77%22.95%16.65%Native American or Alaska Native alone (NH)33018111785460.81%0.42%0.27%0.20%0.11%Asian alone (NH)1,2061,7221,7612,2312,9192.98%4.04%4.13%5.22%6.81%Native Hawaiian or Pacific Islander alone (NH)4965470.11%0.15%0.11%Other race alone (NH)1131181511872930.28%0.28%0.35%0.44%0.68%Mixed race or Multiracial (NH)xx1,8821,6602,334xx4.42%3.88%5.45%Hispanic or Latino (any race)3,4656,0198,69011,50212,1718.55%14.11%20.39%26.89%28.41%Total40,51042,65842,61042,77742,846100.00%100.00%100.00%100.00%100.00%

2020 census

As of the 2020 census, Altadena had a population of 42,846, with a population density of . The census reported that 98.3% of the population lived in households, 1.2% lived in non-institutionalized group quarters, and 0.5% were institutionalized. 99.7% of residents lived in urban areas, while 0.3% lived in rural areas.

The median age was 45.5years; 18.6% of residents were under the age of 18, 7.1% were aged 18 to 24, 23.7% were aged 25 to 44, 30.1% were aged 45 to 64, and 20.5% were 65years of age or older. For every 100 females there were 92.9 males, and for every 100 females age 18 and over there were 89.4 males age 18 and over.

There were 15,429 households, of which 29.7% had children under the age of 18 living in them. Married-couple households represented 50.9%, 15.0% had a male householder with no spouse or partner present, and 28.3% had a female householder with no spouse or partner present. About 22.2% of all households were made up of individuals and 10.6% had someone living alone who was 65 years of age or older. The average household size was 2.73. There were 11,055 families (71.7% of all households).

There were 16,063 housing units at an average density of , of which 3.9% were vacant. Of the 15,429 occupied units, 71.7% were owner-occupied and 28.3% were occupied by renters. The homeowner vacancy rate was 0.6%, and the rental vacancy rate was 3.0%.

+ Racial composition as of the 2020 census Race Number Percent White 19,785 46.2% Black or African American 7,387 17.2% American Indian and Alaska Native 381 0.9% Asian 3,026 7.1% Native Hawaiian and Other Pacific Islander 54 0.1% Some other race 5,485 12.8% Two or more races 6,728 15.7%

2010 census