In 1947, the American Telephone and Telegraph Company (AT&T) devised the first nationwide telephone numbering plan and assigned the original North American area codes.
The state of California was divided into three numbering plan areas (NPAs) with distinct area codes: 213, 415, and 916, for the southern, central, and northern parts of the state, respectively.
[1] As of July 2023, California has 38 active area codes.
Area code 837 is scheduled for overlay on 530 (January 31, 2025), respectively.
Area code 357 will be an overlay in area code 559 starting first quarter of 2025 (https://docs.cpuc.ca.gov/PublishedDocs/Published/G000/M530/K320/530320126.PDF).