In California it is illegal to possess Bufo Alvarius. They have been extirpated from CA. CA Fish and Wildlife has made it illegal to possess in order to protect them from being brought over from AZ (AZ doesn't allow their native herps to be transported out of state). They are also trying to protect any small populations that might be left in CA.
Outside of CA and AZ, it is the responsibility of each state to allow or not allow certain species. Some states do not allow these toads to be kept due to the hallucinogenic properties of their toxin.