Legal Question in Family Law in California

If the 401K was funded with money earned during the marriage it is likely that there is a community property interest in the 401K which would be subject to division in a dissolution proceeding.

Mr. White is correct. More specifically he is entitled to half the money deposited from earnings during the marriage, plus or minus any gain or loss on those funds. Funds and earnings or losses before and after the marriage are yours. As part of the divorce you will want to get a qualified domestic relations order to the holder of the 401k that rolls his share out into an IRA for him. Otherwise you could both face taxes when he gets his share.