California currently utilizes 34 area codes. When first established by AT&T and the Bell System in 1947, 213 covered southern California including Los Angeles, 415 covered northern/central California including San Francisco and Sacramento, and 916 covered northern California but not including Sacramento. The most recently added was 820 in 2018 as an overlay to 805. Today, 760 is the most populated with an estimated 5.7 million of the state's 37.3 million residents.
Sources: North American Numbering Plan Administration (NANPA), telecom providers, and the U.S. Census Bureau.