California businesses accept the U.S. dollar ($). Most businesses also accept major credit cards: Visa, MasterCard, Discover, Diner’s Club, and American Express. ATM and check-cards work at many stores and restaurants, and you’re likely to find ATMs in most every town of any size.
You can change currency in any international airport in the state. Currency exchange points also crop up in downtown San Francisco  and Los Angeles  and at some of the major business hotels in the urban areas.