Your first step is to file a police report to document the activity. Not only will that start the legal process working, but can also help to dispute credit accounts and collections that are put against you based on somebody else's actions. Good luck. Be sure to give the police all the information you have gathered.
See the link below for a compilion of laws and rights regarding identiy theft in California.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.