Cal. Rev. & Tax. Code § 3437

The amount due on any property may be paid until the close of business on June 30 if it was separately valued on the secured roll. If June 30 falls on a Saturday, Sunday, or legal holiday, and payment is received by the close of business on the next business day, redemption penalties shall not attach. If the board of supervisors, by adoption of an ordinance or resolution, closes the county’s offices for business prior to the time of delinquency on the “next business day” or for that whole day, that day shall be considered a legal holiday for purposes of this section. Section 2512 shall apply to remittances made by mail.