20th century

Migration to California accelerated during the early 20th century with the completion of major transcontinental highways like the Lincoln Highway and Route 66. In the period from 1900 to 1965, the population grew from fewer than one million to become the most populous state in the Union. In 1940, the Census Bureau reported California's population as 6.0% Hispanic, 2.4% Asian, and 89.5% non-Hispanic white.^[55]
To meet the population's needs, major engineering feats like the California and Los Angeles Aqueducts; the Oroville and Shasta Dams; and the Bay and Golden Gate Bridges were built across the state. The state government also adopted the California Master Plan for Higher Education in 1960 to develop a highly efficient system of public education.
Meanwhile, attracted to the mild Mediterranean climate, cheap land, and the state's wide variety of geography, filmmakers established the studio system in Hollywood in the 1920s. California manufactured 8.7 percent of total United States military armaments produced during World War II, ranking third (behind New York and Michigan) among the 48 states.^[56] After World War II, California's economy greatly expanded due to strong aerospace and defense industries,^[57] whose size decreased following the end of the Cold War.^[57][58] Stanford University and its Dean of Engineering Frederick Terman began encouraging faculty and graduates to stay in California instead of leaving the state, and develop a high-tech region in the area now known as Silicon Valley.^[59] As a result of these efforts, California is regarded as a world center of the entertainment and music industries, of technology, engineering, and the aerospace industry, and as the United States center of agricultural production.^[60] Just before the "Dot Com Bust" California had the 5th largest economy in the world among nations.^[61] Yet since 1991, and starting in the late 1980s in Southern California, California has seen a net loss of domestic migrants most years. This is often referred to by the media as the California exodus.^[62]
However, during the 20th century, two great disasters happened in California. The 1906 San Francisco earthquake and 1928 St. Francis Dam flood remain the deadliest in U.S history.^[63]