Cal. Rev. & Tax. Code § 50
For purposes of base year values as determined by Section 110.1, values determined for property which is purchased or changes ownership after the 1975 lien date shall be entered on the roll for the lien date next succeeding the date of the purchase or change in ownership. Values determined after the 1975 lien date for property which is newly constructed shall be entered on the roll for the lien date next succeeding the date of completion of the new construction. The value of new construction in progress on the lien date shall be entered on the roll as of the lien date. However, the value of new construction in progress shall not be a base year value until completion of that construction, as described in Section 71.
Ca. Rev. and Tax. Code § 50