In Southern California, from 1870 to 1950, two sectors of the economy interacted to produce major changes in the region. Citrus agriculture and transcontinental railroads defined the economy, landscape, labor, and culture of the Southland. As railroads linked Southern California to the far corners of North America in the 1870s and 1880s, they ended centuries of isolation. They made it possible for growers to ship their goods to the Midwest and Atlantic Coast. Almost simultaneously, the citrus industry expanded in Southern California. Introduced by Spanish friars during the 1800s, orange and lemon growing boomed in the 1870s thanks to the importation of the Washington Navel orange from Brazil. Spreading out from the epicenter of Riverside, the orange empire incorporated portions of Riverside, San Bernardino, Los Angeles, Orange, Ventura, Santa Barbara, San Diego, and Imperial Counties. Railroad companies competed to corner the trafficking of citrus fruits from California, resulting in an extensive network of rails across this orange empire. Although high startup costs were associated with the establishment of an orange grove, lucrative returns, facilitated by railroad connections to markets, led to prosperity in Southern California from the 1890s to the 1950s.

Numerous developments accompanied the intertwined activities of the orange and railroad industries. Technical innovations, such as the invention of refrigerator cars and advanced packing machinery to preserve oranges during transit, facilitated the growth of industry. New cities, devoted almost entirely to citrus cultivation, appeared along the railroad tracks. Railroaders and orange growers worked together to irrigate the parched Southland, and, when necessary, to limit the effects of floods, and promoted the spread of electricity. However, they also brought far more ambivalent consequences. Laborers, often drawn from ethnic minorities, suffered the constant threat of bodily harm and low wages. From the Pullman strike of 1896 to the guerilla war of 1936 in Orange County, railroads and grove owners quashed attempts at organized labor. Railroad and citrus boosters also promoted California as paradise, but minimized the roles of laborers by stereotyping them in advertisements and publications. Despite their gradual decline in the 1950s, these twin industries interacted in a variety of ways, creatively and destructively, overlapping to shape the history of Southern California.