Cal. Rev. & Tax. Code § 3706
If the property is not redeemed before the close of business on the last business day prior to the date of the sale of the property, the tax collector shall sell the property at public auction to the highest bidder at the time and place fixed.
In the case of a sale at public auction, no bid shall be accepted for a sum less than the minimum price approved in the resolution of the board of supervisors; provided, however, the tax collector may reduce such minimum price when a partial redemption has been made under Chapter 2, Part 7, Division 1 of this code, or when a partial cancellation has been made under Chapter 4, Part 9, Division 1 of this code, after such price was fixed, by not more than the ratio that the delinquency on the portion so redeemed or canceled bears to the delinquency upon the whole.
Ca. Rev. and Tax. Code § 3706