Cal. RTC § 4717

(a) If a tax payment which is insufficient to cover the amount of taxes due and payable is received by the tax collector of a county that has elected to follow the procedure authorized by this chapter, the tax collector shall place the tax payment in a trust fund and immediately notify the taxpayer of the deficiency.

(b) In the case of a deficiency in the payment of secured taxes, the taxpayer may pay the balance due until the date on which the property becomes tax defaulted by operation of law. If payment of the balance due is not received on or before that date, the insufficient payment shall be returned to the taxpayer, and shall become tax defaulted in the usual manner as provided in this code.

(c) In the case of a deficiency in the payment of unsecured taxes, the taxpayer may pay the balance due within six months after the date of the insufficient payment. If payment of the balance due is not made within that time, the tax collector or other officer collecting unsecured taxes shall credit the amount of the insufficient payment on the unsecured roll.

(d) If payment of the balance due is made within the time specified in this section, any delinquent penalty which attaches by operation of law shall be computed only upon the additional amount required to bring the payment to a nondelinquent status.

(e) The county auditor shall make the necessary adjustments in the tax rolls and in the tax and penalty charges.

(f) The tax collector may accept payments which are within twenty dollars ($20) of the tax due as payment in full. The auditor or controller shall prescribe methods for accounting and adjusting their accounts in this matter.

(g) The provisions of this section shall become effective in any county when authorized by resolution adopted by majority vote of the board of supervisors of the county.