Cal. Food & Agric. Code § 6025.4
Notwithstanding Section 597u of the Penal Code, carbon monoxide may be used for the control of burrowing rodent pests, provided the following conditions are met:
(a) The carbon monoxide delivery device shall be permanently affixed with a warning label in plain view of the operator that includes, at a minimum, the following information:
DANGER: Carbon monoxide is a poisonous gas that is odorless and colorless. Exposure to carbon monoxide can kill within minutes. Never use in structures inhabited by humans or livestock. The device must be used in accordance with all existing laws and regulations including Chapter 1.5 (commencing with Section 2050) of Division 3 of, known as the California Endangered Species Act, and Sections 4002 and 4003 of, the Fish and Game Code.