If a person dies without a will, with an invalid will, or with a will or trust that does not properly dispose of all the assets, the state of California essentially writes the will. I have found that most people, when given the choice, do not opt for the automatic statutory provisions of the California Probate Code. People have their own ideas. For example, you may prefer to pass your assets on to friends, a partner, or a charity rather than family or distant blood relations.
For a married person who dies:
All community property to the surviving spouse or domestic partner.
All Separate property to the surviving spouse or domestic partner if there are no surviving children, parent, siblings, or children of siblings of the decedent. And here is where there are it depends on the survivors: If there is/are also a surviving child or children: with one child, ½ to the surviving spouse and ½ to the child; with more than one child, 1/3 to the surviving spouse or domestic partner and 2/3 to the children. And if there is a surviving spouse or domestic partner, and no children but the parents are alive, ½ to the surviving spouse or domestic partner and ½ to the parents. If there are no surviving parents of the decedent but there are surviving siblings, the parents’ ½ goes to the siblings or their children.
For the single person who dies, property passes first to the children of the decedent, but if there are no children or grandchildren (“issue”), then to the decedent’s parents, and if no children or surviving parents, to the siblings of the decedent or their children (the nieces and nephews of the decedent).