California Code, Revenue and Taxation Code - RTC § 4524

(a) Upon the receipt by the tax collector of the entire amount of the taxes, assessments, and assigned penalties assigned by a tax certificate, the tax collector shall pay that amount to the holder of the tax certificate, cancel the tax certificate, and enter the fact of the cancellation in the tax certificate record opposite the entry of the sale of the tax certificate. The tax collector shall make the payments from amounts it receives of those taxes, assessments, and assigned penalties, whether those amounts are received by the tax collector by payment of those amounts, by redemption pursuant to Part 7 (commencing with Section 4101), by sale of the parcel pursuant to Chapter 2 (commencing with Section 3436) of Part 6, or otherwise.

(b) If, pursuant to Section 2636, 2708, 2772, or 4143 or otherwise, the tax collector receives only an installment or portion of the amounts in respect of the taxes, assessments, and assigned penalties (or interest in the case of an installment plan of redemption) assigned by a tax certificate, the tax collector shall pay that amount to the holder of the tax certificate and make a corresponding adjustment to the amounts set forth in the tax certificate and the tax certificate record.

(c) If, pursuant to Chapter 3 (commencing with Section 2801) of Part 5 or Chapter 2 (commencing with Section 4131) of Part 7, part of an assessment of tax on a parcel specified in a tax certificate is paid or redeemed, the tax collector shall pay to the holder of the tax certificate that portion of the payments relating to the amounts assigned under the tax certificate and shall adjust the information in the tax certificate and the tax certificate record accordingly.

(d) Any amount collected shall be first applied to the oldest outstanding certificate. The taxpayer shall still be considered delinquent with respect to any unredeemed certificate on that property.

(e) Notwithstanding any other provision of law, any partial payment with respect to a tax certificate, including annual payments from installment plan of redemption, shall be applied to the monthly penalty (or interest in the case of an installment plan of redemption) amount first.

(f) This section shall apply notwithstanding any other provision of Chapter 1C (commencing with Section 4656) or Chapter 1.3 (commencing with Section 4671) of Part 8 or any other provision of this code to the contrary.