Cal. Rev. & Tax. Code § 110.1

(a) For purposes of subdivision (a) of Section 2 of Article XIII A of the California Constitution, “full cash value” of real property, including possessory interests in real property, means the fair market value as determined pursuant to Section 110 for either of the following:
1. (1) The 1975 lien date.
2. (2) For property which is purchased, is newly constructed, or changes ownership after the 1975 lien date, either of the following:
  1. (A) The date on which a purchase or change in ownership occurs.
  2. (B) The date on which new construction is completed, and if uncompleted, on the lien date.
(b) The value determined under subdivision (a) shall be known as the base year value for the property. However, uncompleted new construction shall not acquire a base year value until completed, as described in Section 71.
(c) Notwithstanding Section 405.5, for property which was not purchased or newly constructed or has not changed ownership after the 1975 lien date, if the value as shown on the 1975–76 roll is not its 1975 lien date base year value and if the value of that property had not been determined pursuant to a periodic reappraisal under Section 405.5 for the 1975–76 assessment roll, a new 1975 lien date base year value shall be determined at any time until June 30, 1980, and placed on the roll being prepared for the current year; provided, however, that for any county over four million in population the board of supervisors may adopt a resolution granting the assessor of that county until June 30, 1981, the authority to determine those values. Regardless of the foregoing restrictions, property that escaped taxation for 1975 and was not merely underassessed for that year, shall be added to the roll in any year in which the escape is discovered at its 1975 base year value indexed to reflect inflation as provided in subdivision(f). In determining the new base year value for that property, the assessor shall use only those factors and indicia of fair market value actually utilized in appraisals made pursuant to Section 405.5 for the 1975 lien date. The new base year values shall be consistent with the values established by reappraisal for the 1975 lien date of comparable properties which were reappraised pursuant to Section 405.5 for the fiscal year. In the event that determination is made, no escape assessment may be levied and the newly determined “full cash value” shall be placed on the roll for the current year only; provided, however, the preceding shall not prohibit a determination which is made prior to June 30 of a fiscal year from being reflected on the assessment roll for the current fiscal year.
(d) If the value of any real property as shown on the 1975–76 roll was determined pursuant to a periodic appraisal under Section 405.5, that value shall be the 1975 lien date base year value of the property.
(e) As used in subdivisions (c) and (d), a parcel of property shall be presumed to have been appraised for the 1975–76 fiscal year if the assessor’s determination of the value of the property for the 1975–76 fiscal year differed from the value used for purposes of computing the 1974–75 fiscal year tax liability for the property, but the assessor may rebut that presumption by evidence that, notwithstanding the difference in value, that parcel was not appraised pursuant to Section 405.5 for the 1975–76 fiscal year.
(f) For each lien date after the lien date in which the full cash value is determined pursuant to this section, the full cash value of real property, including possessory interests in real property, shall be adjusted by an inflation factor, which shall be determined as provided in subdivision (a) of Section 51.