Pen. Code, § 3604

(a) The punishment of death shall be inflicted by the administration of a lethal gas or by an intravenous injection of a substance or substances in a lethal quantity sufficient to cause death, by standards established under the direction of the Department of Corrections and Rehabilitation.

(b) Persons sentenced to death prior to or after the operative date of this subdivision shall have the opportunity to elect to have the punishment imposed by lethal gas or lethal injection. This choice shall be made in writing and shall be submitted to the warden pursuant to regulations established by the Department of Corrections and Rehabilitation. If a person under sentence of death does not choose either lethal gas or lethal injection within 10 days after the warden’s service upon the inmate of an execution warrant issued following the operative date of this subdivision, the penalty of death shall be imposed by lethal injection.

(c) Where the person sentenced to death is not executed on the date set for execution and a new execution date is subsequently set, the inmate again shall have the opportunity to elect to have punishment imposed by lethal gas or lethal injection, according to the procedures set forth in subdivision (b).

(d) Notwithstanding subdivision (b), if either manner of execution described in subdivision (a) is held invalid, the punishment of death shall be imposed by the alternative means specified in subdivision (a).

(e) The Department of Corrections and Rehabilitation, or any successor agency with the duty to execute judgments of death, shall maintain at all times the ability to execute such judgments.