California is the most populous state in the United States, and the third largest by area. California is the second most populous sub-national entity in the Americas, behind only São Paulo, Brazil. It is located on the West Coast of the United States, and is bordered by Oregon to the north, Nevada to the northeast, Arizona to the southeast, the Mexican state of Baja California to the south, and the Pacific Ocean to the west. Its four largest cities are Los Angeles, San Diego, San Jose, and San Francisco. The state is home to the nation's second and sixth largest metropolitan areas as well as eight of the nation's fifty largest cities. California has varied climate and geography and a diverse population.
California is the third-largest U.S. state by land area, after Alaska and Texas. Its geography ranges from the Pacific coast to the Sierra Nevada mountain range in the east, to Mojave desert areas in the southeast and the Redwood–Douglas fir forests of the northwest. The center of the state is dominated by the Central Valley, one of the most productive agricultural areas in the world. California is the most geographically diverse state in the nation, and contains the highest (Mount Whitney) and lowest (Death Valley) points in the contiguous United States.
Beginning in the late 18th century, the area known as Alta California was colonized by the Spanish Empire. In 1821, Mexico, including Alta California, became an independent monarchy, then a republic. In 1846 a group of American settlers in Sonoma declared the independence of a California Republic. As a result of the Mexican-American War, Mexico ceded California to the United States. It became the 31st state admitted to the union on September 9, 1850.
In the 19th century, the California Gold Rush brought about dramatic social, economic, and demographic change in California, with a large influx of people and an economic boom that caused San Francisco to grow from a hamlet of tents to a world-renowned boomtown. Key developments in the early 20th century included the emergence of Los Angeles as center of the American entertainment industry, and the growth of a large, state-wide tourism sector. In addition to California's prosperous agricultural industry, other important contributors to the economy include aerospace, petroleum, and information technology. If California were a country, it would rank among the ten largest economies in the world, with a GDP similar to that of Italy. It would be the 35th most populous country.