In 1848, the non-native population of California has been estimated to be no more than 15,000. But after gold was discovered, the population burgeoned with U.S. citizens, Europeans, and other immigrants during the great California Gold Rush. In 1850, California was admitted to the United States as a free state (one in which slavery was prohibited).

The seat of government for California under Mexican rule was located at Monterey from 1777 until 1849, at which time the Constitutional Convention was first held. Among the duties was the task of determining the location for the capital. The first legislative sessions were held in San Jose (1850-1851). Subsequent locations included Vallejo (1852-1853), and nearby Benicia (1853-1854), although these locations eventually proved to be inadequate as well. The capital has been located in Sacramento since 1854.[10]

At first, travel between California and the central and eastern parts of the United States was time-consuming and dangerous. A more direct connection came in 1869 with the completion of the First Transcontinental Railroad. After this rail link was established, hundreds of thousands of U.S. citizens came west, where new Californians were discovering that land in the state, if irrigated during the dry summer months, was extremely well-suited to fruit cultivation and agriculture in general. Citrus was widely grown (especially oranges), and the foundation was laid for the state's prodigious agricultural production.

During the early 20th century, migration to California accelerated 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. From 1965 to the present, the population changed radically and became one of the most diverse in the world. The state is regarded a world center of engineering businesses, the entertainment and music industries, and of U.S. agricultural production