It's legal insofar that if you want to exercise your rights expect to sit in Jail until your lawyer can take it to the Supreme Court. At which point CA will slightly reword the law to intentionally circumvent the Constitutional rights of its citizens.
I have no idea about CA but this is absolutely the case in NYC.[] Dexter Taylor is sitting in jail for a decade for making personal use firearms without a license. No other alleged criminal activity and they never even left his house. During trial, the judge said "the second amendment isn't allowed in my courtroom."*
His lawyer knows they are going to lose all the appeals in New York but basically he has to sit in jail for 3-4 years through the state court system until it can hit federal courts where there is a good chance his case will eventually get overturned.
[] https://en.wikipedia.org/wiki/Dexter_Taylor
* Response to below (my comments are throttled): The argument/reference in his defense, not actual guns.