Altadena is an unincorporated area and census-designated place in Los Angeles County, California, United States, approximately 14 miles (23 km) from the downtown Los Angeles Civic Center, and directly north of the city of Pasadena, California. The population was 42,777 at the 2010 census, up from 42,610 at the 2000 census.
In the mid-1860s, Benjamin Eaton (not to be confused with Coloradan politician Benjamin Eaton) first developed water sources from the Arroyo Seco and Eaton Canyon to 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 was the future sites of these three communities. They hoped to develop and sell this 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 in Arroyo Seco. They had failed 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. This included the land of present day Altadena, but they developed a section further south as Pasadena. In 1881, the land that would later become Altadena was sold to the John and Fred Woodbury, brothers who launched the subdivision of Altadena in 1887. The land remained mostly agricultural; however, several eastern millionaires built mansions along Mariposa Street, and a small community developed through the 1890s and into the next century.
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 good friend Col. G. G. 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.
Over the years Altadena has been subject to attempted annexation by Pasadena. 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.
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. With early 1960s redevelopment in Pasadena, the routing of extensions of 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 Caucasian 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.
The name Altadena derives from the Spanish alta, meaning "upper", and dena from Pasadena; the area is adjacent to, but at a higher elevation than, Pasadena.