California Code, Revenue and Taxation Code - RTC § 24914

(a) If the property was acquired by gift after December 31, 1920, the basis shall be the same as it would be in the hands of the donor or the last preceding owner by whom it was not acquired by gift, except that if such basis (adjusted for the period before the date of the gift as provided in Sections 24916 and 24917) is greater than the fair market value of the property at the time of the gift, then for the purpose of determining loss the basis shall be such fair market value. If the facts necessary to determine the basis in the hands of the donor or the last preceding owner are unknown to the donee, the Franchise Tax Board shall, if possible, obtain such facts from such donor or last preceding owner, or any other person cognizant thereof. If the Franchise Tax Board finds it impossible to obtain such facts, the basis in the hands of such donor or last preceding owner shall be the fair market value of such property as found by the Franchise Tax Board as of the date or approximate date at which, according to the best information that the Franchise Tax Board is able to obtain, such property was acquired by such donor or last preceding owner.

(b) If the property was acquired after December 31, 1920, by a transfer in trust (other than by a transfer in trust by a gift, bequest, or devise), the basis shall be the same as it would be in the hands of the grantor increased in the amount of gain or decreased in the amount of loss recognized to the grantor on such transfer under the law applicable to the year in which the transfer was made.