California Code, Streets and Highways Code - SHC § 9307

In the event of sale by the tax collector of any lot or parcel of land for nonpayment of taxes and of any installment of the reassessment thereon, or of the penalties, interest, or costs thereon, or for nonpayment of any installment, penalties, interest, or costs, then any certificate of sale or any deed issued is primary evidence of the regularity of all proceedings theretofore had, and shall be conclusive evidence of all things of which bonds issued upon the security thereof are conclusive evidence, and prima facie evidence of the regularity of all proceedings subsequent to the issuance of the bonds.