Henry E. Huntington was the nephew of Collis P. Huntington, one of The Big Four, the men instrumental in creating the Central Pacific Railroad (later called Southern Pacific), one of the two railroads that built the transcontinental railway in 1869. Huntington held several executive positions working alongside his uncle with the Southern Pacific Transportation Company. After Collis P. Huntington's death, Henry E. Huntington assumed Collis Huntington's leadership role with Newport News Shipbuilding and Drydock Company in Virginia, and married his widow Arabella Huntington.

In friendly competition with his uncle's Southern Pacific, in 1898, Huntington purchased the narrow gauge, city oriented Los Angeles Railway (LARy) known colloquially as the 'Yellow Car' system. In 1901 Huntington formed the sprawling interurban, standard gauge Pacific Electric Railway (the PE), known more familiarly as the 'Red Car' system, centered at 6th and Main Streets in Los Angeles. This competition with his uncle's Southern Pacific could be achieved by the need for passenger friendly streetcars, on 24/7 schedules, that the railroads couldn't match—and by the boom in Southern California land development—where houses were built in distant places, like Orange County's Huntington Beach, a Huntington sponsored development, where streetcars served passenger needs that the railroads had never considered.

By 1910, the Huntington trolley systems stretched over approximately 1,300 miles (2,100 km) of southern California.[2] At its most robust size, the system contained over 20 streetcar lines and 1,250 trolleys, most running through the core of Los Angeles and serving such nearby neighborhoods as Echo Park, Westlake, Hancock Park, Exposition Park, West Adams, the Crenshaw district, Vernon, Boyle Heights and Lincoln Heights; The system integrated the 1902 acquisition, the Mount Lowe Scenic Railway above Altadena, California in the San Gabriel Mountains.[3]

In 1905 Huntington, A. Kingsley Macomber, and William R. Staats developed the Oak Knoll subdivision, located to the west of his San Marino estate in the oak-covered hilly terrain near Pasadena.

In 1906 Huntington, along with Frank Miller, owner of the Mission Inn, and Charles M. Loring, formed the Huntington Park Association, with the intent to purchase Mount Rubidoux in Riverside, build a road to the summit, and develop the hill as a park to benefit the city of Riverside.[4] The road was completed in February 1907.[5] The property was later donated to the city of Riverside by the heirs of Frank Miller, and today the hill is a 161-acre (0.65 km2; 0.252 sq mi) city park.