Cal. Pub. Util. Code § 120452

Violation of any ordinance, rule, or regulation enacted by the board prohibiting the unauthorized entering into, climbing upon, holding onto, or in any manner attaching oneself to vehicles operated upon exclusive public mass transit guideways owned or controlled by the board, is an infraction punishable by a fine not exceeding fifty dollars ($50), except that a violation by a person, after the first conviction under this section, is a misdemeanor punishable by a fine not exceeding five hundred dollars ($500) or by imprisonment in a county jail not exceeding six months, or by both that fine and imprisonment.