California Code, Revenue and Taxation Code - RTC § 11293

In making an assessment, the board shall determine the average number of each class of private railroad cars physically present in the state in the calendar year immediately preceding the fiscal year in which the tax is imposed upon the basis of car days. The board shall multiply the average number so determined by the value of a car of that class as determined under Section 11292 and use the product for the assessment of the cars.