As I used to be a Californian, I still keep up to date on happenings from my old state.
The NRA sent out the following notice today:

Senate Bill 776, sponsored by State Senator Loni Hancock (D-9), has been introduced in Sacramento.? The bill has been assigned to the Senate Public Safety Committee and could be heard on Tuesday, April 21 or Tuesday, April 28.
Simply put, SB776 would mandate the registration of all magazines capable of holding more than ten rounds of ammunition.? The possession of unregistered magazines would be a crime and punishable up to a year in prison.

Not this crap again.
California’s prohibited the purchase or import of magazines with a capacity greater than 10 rounds since 2000 or so, which was in the middle of the now-expired federal AWB. I’ve not seen a single magazine that has a serial number or some other unique marking that could be provided to authorities.
In addition, they implemented rather draconian restrictions on scary-looking guns: new ownership is prohibited, transfer is prohibited (even if the registered owner dies) — the gun must either be removed from the state or destroyed. Of course, not many owners of such firearms bothered to register their guns.
The guns themselves are already heavily regulated, as of January 2010 all handguns must be equipped to apply microstamps to cartridge cases, and proposals to regulate, register, or otherwise restrict ordinary ammunition have also been proposed. In short, California has some of the most onerous gun laws in the nation.
What legitimate reason do they have for wanting to register magazines? What purpose would registering magazines serve? I can’t think of a single one. Criminals are already prohibited from owning guns, and the Fifth Amendment enables them to avoid registration of guns or magazines due to the fact that it would cause them to self-incriminate.
Of course, any registration or prohibition of magazines would be utterly useless: California borders Oregon, Nevada, Arizona, and Mexico. The first three states have essentially no limitiations on magazines, and Mexico’s just a free-for-all. Criminals would have no problems acquiring magazines, regardless of any restrictions in California. Once again, only law-abiding citizens would be affected.