Cal. Government Code § 34090.8

(a) When installing new security systems, a transit agency operated by a city or city and county shall only purchase and install equipment capable of storing recorded images for at least one year, unless all of the following conditions apply: (1) The transit agency has made a diligent effort to identify a security system that is capable of storing recorded data for one year. (2) The transit agency determines that the technology to store recorded data in an economically and technologically feasible manner for one year is not available. (3) The transit agency purchases and installs the best available technology with respect to storage capacity that is both economically and technologically feasible at that time. (b) Notwithstanding any other provision of law, video recordings or other recordings made by security systems operated as part of a public transit system shall be retained for one year, unless one of the following conditions applies: (1) The video recordings or other recordings are evidence in any claim filed or any pending litigation, in which case the video recordings or other recordings shall be preserved until the claim or the pending litigation is resolved. (2) The video recordings or other recordings recorded an event that was or is the subject of an incident report, in which case the video recordings or other recordings shall be preserved until the incident is resolved. (3) The transit agency utilizes a security system that was purchased or installed prior to January 1, 2004, or that meets the requirements of subdivision (a), in which case the video recordings or other recordings shall be preserved for as long as the installed technology allows.