From Wikipedia:
For example, in California, cities which have not adopted a charter are organized by state law. Such a city is called a General Law City, which will be managed by a 5-member city council.
A city organized under a charter may choose different systems, including the "strong mayor" or "city manager" forms of government.
One example of abuse of the charter system was in Bell, California. The charter was created after a little-noticed special election, where few voters understood what becoming a charter city meant. After a charter was approved, state laws limiting city salary no longer applied and City Manager Robert Rizzo gave himself a salary of $1.5 million for managing a city of about 36,000 people.
As of June 2008, 112 of California's 478 cities are charter cities. A few examples include Newport Beach, Huntington Beach, and Irvine.
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