They have a list of acceptable firearms.
If your firearm isn't on the list, it's not legal.
It's not quite that simple. If a HANDGUN is not on the list, it is not legal for a DEALER to SELL. It is still quite legal to
own, even if it is not on the list.
Frpm the certified handguns list:
http://certguns.doj.ca.gov/
"Effective January 1, 2001, no handgun may be manufactured within California, imported into California for sale, lent, given, kept for sale, or offered/exposed for sale unless that handgun model has passed firing, safety, and drop tests and is certified for sale in California by the Department of Justice. Private party transfers, curio/relic handguns, certain single-action revolvers, and pawn/consignment returns are exempt from this requirement."
Please note the emphasis on
sales, not
possession and the private party sale exemption.
When moving into California, you wlill be required to register your HANDGUNS:
http://ag.ca.gov/firearms/pubfaqs.php#24
"I am moving into California and I own several handguns. What are the new-resident registration requirements?
You are considered to be a personal handgun importer as defined by California law. You may bring all of your otherwise California-legal firearms with you, but you must report all of your handguns to the DOJ within 60 days as required utilizing the
New Resident Handgun Ownership Report. [PDF 518 kb / 2 pg] You are not required to report rifles or shotguns. You may not bring ammunition feeding devices with a capacity greater than ten rounds, machineguns, or assault weapons into California.
(PC sections 12001(n), 12072(f)(2))
Disclaimer: I am not a lawyer, I am especially not
your lawyer, take all legal advice on the internet with a grain of salt, including mine. Contact the ATF / your state DOJ directly and get their advice
in writing. Then follow it.