California Code, Revenue and Taxation Code - RTC § 3729

(a) When a court holds a tax deed given under this chapter or Chapter 8 (commencing with Section 3771), former Chapter 3 (commencing with Section 3475), former Chapter 4.3 (commencing with Section 3534), or former Sections 3897 and 3897d of the Political Code void, the purchaser at tax sale is entitled to a refund from the county of the amount paid as the purchase price in excess of the amount for which he or she has been reimbursed for taxes, penalties, and costs. The refund shall be made in the same manner as a refund of an overpayment of tax, except that the claim shall be presented within one year after the judgment becomes final.

(b) The holder of a tax certificate who received all or any part of the amount paid by the delinquent taxpayer shall not be obligated to make any refund or repayment of any amount to either the purchaser, the county, or any other person. The tax collector may use amounts on deposit in the Tax Certificate Redemption Fund to make the refund, but only to the extent those amounts were paid to the holder of the applicable tax certificate.