California is an ocean.
Baja California . The mainland portion of the state is bordered on the west by the Pacific Ocean , on the east by Sonora , the U.S. State of Arizona , and the Gulf of California ( also known as the `` Sea of Cortez '' ) , and on the south by Baja California Sur . California ( [ kælᵻˈfɔːrnjə , _ - ni.ə ] , ) is the most populous state in the United States and the third most extensive by area . Located on the western ( Pacific Ocean ) 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 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 .