Claim: California contains a valley.

California -LRB- -LSB- kælᵻˈfɔːrnjə , _ - ni.ə -RSB- , -RRB- is the most populous state in the United States and the third most extensive by area . Located on the western -LRB- Pacific Ocean -RRB- coast of the U.S. , California is bordered by the other U.S. states of Oregon , Nevada , and Arizona and shares an international border with the Mexican state of Baja California . The state capital is Sacramento . Los Angeles is California 's most populous city , and the country 's second largest after New York City . The Greater Los Angeles Area and the San Francisco Bay Area are the nation 's second - and fifth-most populous urban regions , respectively . California also has the nation 's most populous county , Los Angeles County , and its largest county by area , San Bernardino County .   California 's diverse geography ranges from the Pacific Coast in the west to the Sierra Nevada mountain range in the east ; and from the redwood -- Douglas fir forests in the northwest to the Mojave Desert in the southeast . The Central Valley , a major agricultural area , dominates the state 's center . Though California is well-known for its warm Mediterranean climate , the large size of the state means it can vary from moist temperate rainforest in the north , to arid desert in the interior , as well as snowy alpine in the mountains .   What is now California was first settled by various Native American tribes before being explored by a number of European expeditions during the 16th and 17th centuries . The Spanish Empire then claimed it as part of Alta California in their New Spain colony . The area became a part of Mexico in 1821 following its successful war for independence , but was ceded to the United States in 1848 after the Mexican -- American War . The western portion of Alta California then was organized as the State of California , and admitted as the 31st state on September 9 , 1850 . The California Gold Rush starting in 1848 led to dramatic social and demographic changes , with large-scale emigration from the east and abroad with an accompanying economic boom .   If it were a country , California would be the 6th largest economy in the world and the 35th most populous . It is also regarded as a global trendsetter in both popular culture and politics , and is the origin of the film industry , the hippie counterculture , the Internet , and the personal computer , among others . Fifty-eight percent of the state 's economy is centered on finance , government , real estate services , technology , and professional , scientific and technical business services . The San Francisco Bay Area has the nation 's highest median household income by metropolitan area , and is the headquarters of three of the world 's largest 40 firms by revenue , Chevron , Apple , and McKesson . Although it accounts for only 1.5 percent of the state 's economy , California 's agriculture industry has the highest output of any U.S. state .