Cal. Health and Safety Code § 7100.1

(a) A decedent, prior to death, may direct, in writing, the disposition of his or her remains and specify funeral goods and services to be provided. Unless there is a statement to the contrary that is signed and dated by the decedent, the directions may not be altered, changed, or otherwise amended in any material way, except as may be required by law, and shall be faithfully carried out upon his or her death, provided both of the following requirements are met: (1) the directions set forth clearly and completely the final wishes of the decedent in sufficient detail so as to preclude any material ambiguity with regard to the instructions; and, (2) arrangements for payment through trusts, insurance, commitments by others, or any other effective and binding means, have been made, so as to preclude the payment of any funds by the survivor or survivors of the deceased that might otherwise retain the right to control the disposition. (b) In the event arrangements for only one of either the cost of interment or the cost of the funeral goods and services are made pursuant to this section, the remaining wishes of the decedent shall be carried out only to the extent that the decedent has sufficient assets to do so, unless the person or persons that otherwise have the right to control the disposition and arrange for funeral goods and services agree to assume the cost. All other provisions of the directions shall be carried out. (c) If the directions are contained in a will, they shall be immediately carried out, regardless of the validity of the will in other respects or of the fact that the will may not be offered for or admitted to probate until a later date.