California Revenue & Taxation Code
Cal. Rev. & Tax. Code § 9258
Official textleginfo.legislature.ca.gov
On or after January 1, 1976, any person who equips a vehicle with a system using liquefied petroleum gas, compressed natural gas or liquid natural gas to propel the vehicle, or who transfers any vehicle so equipped shall notify the board within 10 days after so equipping or transferring the vehicle.
Source: view the official text