California (IPA: /ˌkælɪˈfɔrnjə/) is a state located on the West Coast of the United States, along the Pacific Ocean. It is bordered by Oregon to the north, Nevada to the east, and Arizona to the southeast, as well as by Baja California in Mexico to the south. The most populous U.S. state, California's capital city is Sacramento, and its four largest cities are Los Angeles, San Diego, San Jose, and San Francisco. California is known for its varied climate and geography, as well as for its ethnically diverse population. The state is divided into 58 counties.Before becoming a part of the United States, Alta California was colonized by the Spanish Empire, beginning in 1769. Alta California became a part of the newly independent nation of Mexico in 1821, and remained so until 1846. That year, an independent California Republic was declared. The Republic's first and only president was William B. Ide, who played a pivotal role during the Bear Flag Revolt. His term lasted twenty-five days and concluded when California was occupied by U.S. forces during the Mexican-American War. Under the Treaty of Guadalupe Hidalgo of 1848, Mexico formally ceded California to the United States. California was admitted to the Union as the 31st state on September 9, 1850.California is the third largest U.S. state by land area; it contains a diverse geography, which ranges from the sandy and rocky beaches of the Pacific coast, to the rugged snow-capped Sierra Nevada mountains in the east, to desert areas in the southeast and the forests of the northwest. The center portion of the state is dominated by the Central Valley, one of the most productive agricultural areas in the world and the largest of any U.S. state. The Sierra Nevada mountains contain Yosemite Valley, famous for its glacially-carved domes, and Sequoia National Park, home to the giant sequoia trees, the largest living organisms on Earth. The state is home to Mount Whitney, the highest point in the contiguous United States, as well as the second lowest and hottest place in the Western Hemisphere, Death Valley. Many of the trees located in the California White Mountains are the oldest in the world; one Bristlecone pine has an age of 4,700 years.The California Gold Rush began in 1848, dramatically changing California with a large influx of people and an economic boom. The early 20th century was marked by Los Angeles becoming the center of the entertainment industry, in addition to the growth of a large tourism sector in the state. Along with California's prosperous agricultural industry, other industries include aerospace, petroleum, and computer and information technology. California ranks among the ten largest economies in the world, and were it a separate country, it would be 34th amongst the most populous countries, just behind Poland, as well as the world's sixth-largest economy.