Gun yes, magazine no. thats basically the blunt answer. if you plan to do anything such as open carry its not worth the risk. pick up some 10 rd mags for 20 bucks or so and you will be good, surprisingly CA does not require handgun registration... even tho many police officers do not understand that. might be worthwhile to print out DOJ's page on it just to cover ur rear... better to be over prepared then under.
There is no firearm registration requirement in California except for assault weapon owners and personal handgun importers. However, you may submit a Firearm Ownership Record to the DOJ for any firearm you own. Having a Firearm Ownership Record on file with the DOJ may help in the return of your firearm if it is lost or stolen. With very few and specific exceptions, all firearm transactions must be conducted through a firearms dealer.