That requires an OpLaw form to be filled with the state DoJ, see PC 27875(a)(3). And it also must be "infrequent", meaning it counts towards the limit of 5 per year; see 27875(a)(1).
There is a very interesting question, namely whether guns can be community property in California or not. One side of the argument is that in most cases, most property acquired by a married couple is automatically community property. The other side of the argument is that guns are titled (like real estate or vehicles), and the California DROS system and underlying law does not allow that title to be held by two individuals (unlike real estate or vehicles, where they can be, and in the case of real estate by default are unless explicitly stated and signed off otherwise). I've never seen that conundrum fully explained in a legal text, but I think the answer is roughly the following: While only one spouse is listed on the DROS and AFS paperwork, the value of the gun is usually held jointly; in case the assets need to be separated (like in a divorce), one side will get the gun, the other side will have to be reimbursed for half the value.