California is a community property state. What this means for those who are married or who are registered partners is that generally any asset acquired during marriage or any debt incurred during marriage by either spouse belongs to both spouses. There are some exceptions, such as gifts, inheritance, things excluded by a prenuptial agreement, things that were transmuted to one spouse by another spouse, etc. Furthermore, in California both spouses contract toward each other obligations of mutual respect, fidelity, and support and each spouse is subject to the general rules governing fiduciary relationships that imposes a duty of the highest good faith and fair dealing on each spouse.
During a divorce or legal separation, the Court is obligated to equally divide the community assets and the community debts between the spouses.