Cal. Sts. & High. Code § 10413

The tax collector shall sell separately each parcel of land in the published notice on which the assessment remains unpaid, or so much of it as is necessary to realize the amount assessed against the parcel and penalties and costs, and fifty cents ($0.50) for a certificate of sale. If there is no other purchaser for any lot or parcel of land so offered for sale, it shall be struck off to the city as purchaser.