Any person who is not an FFL dealer  in any state can ship a firearm to a FFL dealer in California.  Any unlicensed person can ship a C&R eligible firearm to an FFL Dealer or a C&R licensee in California.  The only exception to this is that C&R handguns must be shipped to an FFL dealer.   Anyone can send an antique firearm (1898 and earlier) without restriction to any buyer in California.  

A licensed dealer shipping to a licensed dealer in California  must secure a California Firearms License Check on the dealer to whom he is shipping.  This applies only to FFL dealers and not to private persons.  For dealers, there is no cost to sign up with the state or to verify a California license.  There is no charge for obtaining an approval number prior to shipping to California and it takes less than one minute on line!

Knowing what may or may not be sold in California is the responsibility of the California dealer.  It is not up to sellers in other states, licensed or not, to determine whether the firearm they have is on the roster of handguns approved for sale in California or an "assault rifle" .  The dealer will transfer the gun in compliance with California law.  Just because a handgun is not on the approved list does not mean a dealer may not receive it or sell it.  

California Department of justice has an excellent web link  which has clear answers to most questions about California firearms sales:  (You need to Login or Register to view media files and links)

Another helpful site is:  (You need to Login or Register to view media files and links)

Thanks to ACGould