M1 carbines are legal in calif., for now at least. The mags are another matter, no mags over 10 rounds.
I think the mag restriction only applies to weapons made after a certain date, other wise they would have had to grandfather the law and I believe that is illegal. It wouldn’t hurt for MistrX to check on line to see if this is the case or not.
FYI, the normal mag is 15 rounds.