California Code, Health and Safety Code - HSC § 11365

(a) It is unlawful to visit or to be in any room or place where any controlled substances which are specified in subdivision (b), (c), or (e), or paragraph (1) of subdivision (f) of Section 11054, specified in paragraph (14), (15), or (20) of subdivision (d) of Section 11054, or specified in subdivision (b) or (c) or paragraph (2) of subdivision (d) of Section 11055, or which are narcotic drugs classified in Schedule III, IV, or V, are being unlawfully smoked or used with knowledge that such activity is occurring.

(b) This section shall apply only where the defendant aids, assists, or abets the perpetration of the unlawful smoking or use of a controlled substance specified in subdivision (a). This subdivision is declaratory of existing law as expressed in People v. Cressey (1970) 2 Cal. 3d 836.