Cal. Rev. & Tax. Code § 38108

“Scaling date” means the date when the quantity of timber harvested, by species, is first definitely determined.

Except for national forest timber, the scaling date shall be no later than the date of delivery of the felled trees to the storage or wood-processing area, whichever is first, or an alternative approved by the board. For national forest timber, the definitely determined timber volume included in forest service, United States Department of Agriculture, billing statements to timber sale contract holders, or an alternative approved by the board after a public hearing, shall be the basis for tax payment.