California Code, Revenue and Taxation Code - RTC § 401.4

When valuing an owner-occupied single-family dwelling and the land on which it is situated that may be required for the convenient occupation and use of such dwelling, if such dwelling is on land which is zoned exclusively for single-family home use or which is zoned for agricultural use where single-family homes are permitted, the assessor shall not value the land at any value greater than that which would reflect the use of the land as a site for a single-family dwelling.

As used in this section, owner-occupied single-family dwelling means any single-family dwelling occupied by an owner thereof as his principal place of residence on the lien date.