Bayonets are perfectly OK.
The only restriction on the SKS under CA state law is that any SKS that actually is an SKS may not have a detachable magazine, and you're limited to 10 rounds. An example of an SKS that's not an SKS would be the Yugos.... Technically, and this matters under CA law, that's a "Zastava Carbine Model 59" and a "Zastava Carbine Model 59/66"... not an SKS.
Since SKS strippers are cheap, and SKS detachable mags all suck, this isn't all that much of a burden for the SKS owner. Not that it should be the law, but in this particular case, it doesn't make anything difficult.
Because it's a fixed magazine, you can do almost whatever else you want to (922(r) still applies, of course)... except put a grenade launcher on it. That's a "destructive device" under CA law, even though you can't get grenades.
That makes no sense, so don't try.
Also bear in mind that unless the firearm is over 50 years old, it is not considered a Curio or Relic under CA law, and would have to be transferred by an FFL. Person-to-person transfer fees are regulated by law here, although a lot of dealers hope that their customers don't know that, and try to charge the same price for a PPT as they do for an FFL transfer. That can cost them their license. If you encounter this, politely let them know first. I wouldn't go calling the DOJ firearms division unless their response really, really warrants it. Which has happened.
If the firearm is more than 50 years old, a direct face-to-face transfer is legal under CA law.
You have to know all this stuff because, under Federal law, a transfer of a long gun between residents of different states must be legal in both states.
So the transfer itself can be a little weird, but there's nothing illegal in California about the gun itself.
And that includes the bayonet. You do not need to remove it.
--Shannon