Cal. Rev. & Tax. Code § 2635

When the amount of taxes paid exceeds the amount due by more than twenty dollars ($20), the tax collector shall send notice of the overpayment to the taxpayer. The notice shall be mailed to the taxpayer’s last known address and shall state the amount of overpayment and that a refund claim may be filed pursuant to Chapter 5 (commencing with Section 5096) of Part 9.