California Code, Probate Code - PROB § 6110

(1) By the testator.

(2) In the testator's name by some other person in the testator's presence and by the testator's direction.

(3) By a conservator pursuant to a court order to make a will under Section 2580.

(c)(1) Except as provided in paragraph (2), the will shall be witnessed by being signed, during the testator's lifetime, by at least two persons each of whom (A) being present at the same time, witnessed either the signing of the will or the testator's acknowledgment of the signature or of the will and (B) understand that the instrument they sign is the testator's will.

(2) If a will was not executed in compliance with paragraph (1), the will shall be treated as if it was executed in compliance with that paragraph if the proponent of the will establishes by clear and convincing evidence that, at the time the testator signed the will, the testator intended the will to constitute the testator's will.