Yes. The applicable provisions of law are found in Business & Professions Code sections 25657 through 25666.5. Probably there rather than the Health & Safety or the Penal Code because so much of has to do with the licensing and regulation of alcoholic beverage sales.
California allows minors between 18 and 20, inclusive, to consume alcoholic beverages in a private, non-beverage-selling setting with or without parental consent, and for religious, medical or educational purposes. "Educational purposes" does not include getting smashed to find out what it's like.
Previous answers suggesting possession was always illegal, one of which was mine, were partly wrong. Possession of alcoholic beverages by a minor is only illegal in a public place or in public view.
The laws are a bit lengthy and complex, and you may want to look up and read the provisions of the code yourself. Also, there are several Web sites you can find on Google by using search terms including minor, alcohol, consume, parent, California, etc. in various combinations.
