Are there any clubs/competitions in California that is open for anyone?

State and County fairs are typically open to all applicants and will usually have competitions for art and music. For engineering, I suggest you look up local and state science fairs. Of course you can always start with community youth clubs and classes which you can often find on your city's website. You can also join clubs at school, I would suggest you look for Art club, NASA HUNCH, TSA, and Band/Orchestra. If your school doesn't offer those clubs/organizations you can often start your own as long as you have a teacher sponsor. If you are home schooled it is state law to allow home schooled kids to join clubs and compete in sports at their home high school. I hope this helps!