The first thing you should do is contact the DMV and find out who the car belongs to. If it has a junk or salvage title you would need to get it retitled and this requires forms and for you to actually buy the car from the owner.
You petition your local authorities on the application. In your case a unkempt vehicle. California is very strict on the fact and will work with you in any means to remove the car. Assure them you want to title it.