California Code, Revenue and Taxation Code - RTC § 75.10

(a) Commencing with the 1983-84 assessment year and each assessment year thereafter, whenever a change in ownership occurs or new construction resulting from actual physical new construction on the site is completed, the assessor shall appraise the property changing ownership or the new construction at its full cash value (except as provided in Section 68 and subdivision (b) of this section) on the date the change in ownership occurs or the new construction is completed. The value so determined shall be the new base year value of the property or the new construction.

(b) For purposes of this chapter, “actual physical new construction” includes the removal of a structure from land. The new base year value of the remaining property (after the removal of the structure) shall be determined in the same manner as provided in subdivision (b) of Section 51.

(c) For purposes of this section, “actual physical new construction” includes the discovery of previously unknown reserves of oil or gas.