Since the custody was determined in AZ, that court has original jurisdiction and California courts cannot modify the custody order except in certain cases. However, there are exceptions wherein you may be able to file for a custody modification in California should you meet certain conditions. For example, if AZ court determines it no longer has exclusive and continuing jurisdiction, or if a California court would be a more convenient forum. Speak with a family law attorney so that you can discuss what options are available for you depending on the facts of your case.