Cal. Health & Safety Code § 7150.30

(a) An individual may refuse to make an anatomical gift of the individual’s body or part by any of the following:
1. (1) A record signed by either of the following:
  1. (A) The individual.
  2. (B) Subject to subdivision (b), another individual acting at the direction of the individual if the individual is physically unable to sign.
2. (2) The individual’s will, whether or not the will is admitted to probate or invalidated after the individual’s death.
3. (3) Any form of communication made by the individual during the individual’s terminal illness or injury addressed to at least two adults, at least one of whom is a disinterested witness. The witnesses shall memorialize this communication in a writing and sign and date the writing.
(b) A record signed pursuant to subparagraph (B) of paragraph (1) of subdivision (a) shall comply with both of the following:
1. (1) It shall be witnessed by at least two adults, at least one of whom is a disinterested witness, who have signed at the request of the individual.
2. (2) It shall state that it has been signed and witnessed as provided in paragraph (1).
(c) An individual who has made a refusal may amend or revoke the refusal by any of the following:
1. (1) In the manner provided in subdivision (a) for making a refusal.
2. (2) By subsequently making an anatomical gift pursuant to Section 7150.20 that is inconsistent with the refusal.
3. (3) By destroying or canceling the record evidencing the refusal, or the portion of the record used to make the refusal, with the intent to revoke the refusal.
(d) Except as otherwise provided in subdivision (h) of Section 7150.35, in the absence of an express, contrary indication by the individual set forth in the refusal, an individual’s unrevoked refusal to make an anatomical gift of the individual’s body or part bars all other persons from making an anatomical gift of the individual’s body or part.
(e) Notwithstanding any provision to the contrary, including, but not limited to, Section 7150.40, only an individual shall make an anatomical gift of all or part of that individual’s body or pacemaker, if it is made known that the individual, at the time of death, was a member of a religion, church, sect, or denomination that relies solely upon prayer for healing of disease or that has religious tenets that would be violated by the disposition of the human body or parts or pacemakers for the purposes of transplantation, therapy, research, or education.