California essentially has two classifications of prohibited weapons, with a degree of overlap. They are:
Weapons which are banned by characteristic - i.e. detachable magazine + pistol grip
Weapons which are banned by make/model - i.e. the Armalite AR-10.
This is a listing of weapons which are banned by make/model - this list can, as of Jan 1st 2007, no longer be updated by the Department of Justice. It could, however, be updated by legislation in the future.
The characteristics ban is discussed here. Notwithstanding, any AR/AK receiver, for which both the make and model does not appear on this list, is by definition not illegal.
AR/AK rifles which are banned by name in California