"Eureka, I have found it" is the apt motto for the nation's most populous state, home to one in eight Americans. The gold rush of 1849 created California's image as a promised land. By 1900 almost half the population was clustered around San Francisco and Los Angeles, each the focus of intense competition for water.

In 1913 the Los Angeles Aqueduct began tapping water from Owens Valley to feed the city's continued unchecked growth. In 1934 San Francisco satisfied its thirst with water from Hetch Hetchy Reservoir, a project that spawned the modern conservation movement. The Colorado River Aqueduct eased the water cravings of burgeoning southern California in the 1940s. The state's largest water transfer—the Central Valley Project—greens some 128,000 square kilometers in the San Joaquin and Sacramento Valleys, where migrant farm laborers find seasonal work.

More immigrants reside here than in any other state, and nearly half of all Californians are immigrants or the children of immigrants. Between 1990 and 2000, California's population increased by 4.1 million. More than 90 percent of the state is urban. Among leading industries is the manufacture of high-tech equipment, centered in the areas of biotechnology, aerospace-defense, and computers.