California Code, Penal Code - PEN § 27880

(a) The loan is to a spouse, registered domestic partner, or any of the following relations, whether by consanguinity, adoption, or steprelation:

(b) The loan is infrequent, as defined in Section 16730.

(c) The loan is for any lawful purpose.

(d) The loan does not exceed 30 days in duration.

(e) Until January 1, 2015, if the firearm is a handgun, the individual being loaned the firearm shall have a valid handgun safety certificate.  Commencing January 1, 2015, for any firearm, the individual being loaned the firearm shall have a valid firearm safety certificate, except that in the case of a handgun, an unexpired handgun safety certificate may be used.

(f) If the firearm being loaned is a handgun, the handgun is registered to the person making the loan pursuant to Section 11106.