From Reason:

Under the latest definition from California, all centerfire semiautomatic rifles are prohibited if they:
 Are on a list that bans guns by make and model, OR
 Have a fixed (nondetachable) magazine over 10 rounds, OR
 Use detachable magazines, and have one of the following features: a pistol grip
that protrudes conspicuously beneath the action of the weapon; a forward pistol grip; a thumbhole stock; a folding or telescoping stock; or a “flash suppressor.”