Cal. Revenue and Taxation Code - RTC § 16860. Section 16860.
Within four years from the last date prescribed for filing the return or within one year from the date the tax was paid, or within 90 days after a determination under Section 16851 is issued, whichever is later, any person who has paid the tax may bring an action against the state in the superior court having jurisdiction to have the tax refunded, in whole or in part.