If you die without a will and your assets are not otherwise designated so that a probate proceeding is required, your property will be distributed to your relatives in the order outlined by state law. California has recently devised a distribution system for intestate succession of registered domestic partners. If you have absolutely no relatives, your property will go to the State.
If you are a single person with children and you die without a will, then your entire estate will go to your children.
If you are single with no children and you die without a will, your estate will be divided between your parents or 100% to the surviving parent. If both of your parents are deceased, then the estate will be divided among your siblings (or the issue of deceased siblings), if you don't have siblings, then to your nieces and nephew, and so on down the family line.
If you are married with children and pass away without a will, your ½ of the community property interest will be passed to your spouse at your death. Now your spouse will own 100% of the community property. If you have separate property, the property will be distributed to your spouse and your children. If you have one child, the separate property will be distributed evenly between your spouse and your child. If you have more than one child, your spouse will receive 1/3 of your separate property and the remaining two-thirds will be distributed in equal shares to your children (or the issue of deceased children).
If you are married and have no children when you die without a will, your spouse will receive your half interest in any community property you hold. If you own separate property, your spouse will receive only half of that separately owned property. The other half will generally go to your living heirs, first your parents and then you siblings.
If you are a domestic partner and you die without a will, trust or other estate plan, your surviving domestic registered partner will inherit a portion of your estate provided that both parties are registered with the California Secretary of State as domestic partners. The portion of the estate your surviving domestic partner will be entitled to will depend on whether you have surviving children or other relatives.