Cal. Rev. & Tax. Code § 51
(a) For purposes of subdivision (b) of Section 2 of Article XIII A of the California Constitution, for each lien date after the lien date in which the base year value is determined pursuant to Section 110.1, the taxable value of real property shall, except as otherwise provided in subdivision (b) or (c), be the lesser of:
(1) Its base year value, compounded annually since the base year by an inflation factor, which shall be determined as follows:
(b) If the real property was damaged or destroyed by disaster, misfortune, or calamity and the board of supervisors of the county in which the real property is located has not adopted an ordinance pursuant to Section 170, or any portion of the real property has been removed by voluntary action by the taxpayer, the taxable value of the property shall be the sum of the following:
(2) The lesser of its base year value of improvements determined pursuant to paragraph (1) of subdivision (a) or the full cash value of improvements determined pursuant to paragraph (2) of subdivision (a).
In applying this subdivision, the base year value of the subject real property does not include that portion of the previous base year value of that property that was attributable to any portion of the property that has been destroyed or removed. The sum determined under this subdivision shall then become the base year value of the real property until that property is restored, repaired, or reconstructed or other provisions of law require establishment of a new base year value.