California is the most heavily populated state of the United States. Situated on the Pacific coast of North America, it is surrounded by Oregon, Nevada, Arizona and Mexico. The state's four largest cities are Los Angeles, San Diego, San Jose and San Francisco. California is recognized for its satisfying climate and culturally diverse population. The state has 58 counties. Settled by indigenous people for millennia, California was first colonized by the Spanish in 1769 and after Mexican independence in 1821, continued as part of Mexico. Following a short period as the independent California Republic in 1846, California was annexed by the United States that same year, and was admitted to the Union as the thirty-first state on September 9, 1850. California's assorted geography ranges from the sandy beaches of the Pacific to the rugged, snow-capped Sierra Nevada mountains in the east. The central portion of the state is dominated by the Central Valley, one of the most vital agricultural areas in the country. The Sierra Nevada contain Yosemite Valley, famous for its glacially-carved domes, and Sequoia National Park, home to the largest living organisms on Earth, the Giant Sequoia trees, and the highest point in the contiguous United States, Mount Whitney. The tallest living things on Earth, ancient Redwood trees, dot the Northern California coastline. California is also home to the lowest and hottest place in the Western Hemisphere, Death Valley. Bristlecone pines located in California's White Mountains are the oldest known trees in the world; one has an age of 4,700 years. The California Gold Rush, beginning in 1848 dramatically changed California with an influx of population and an economic boom. The early part of the 20th century was marked by California's becoming the center of the entertainment industry, in addition to the beginning of growth of a large tourism sector. The Central Valley is home to California's important large agricultural industry. Other important industries have included the aerospace and oil industries. In recent decades, California has become a global leader in computers and information technology. Indeed, if California were a country, it would rank among the largest 10 economies of the world.