Cal. Rev. & Tax. Code § 6396
There are exempted from the computation of the amount of the sales tax the gross receipts from the sale of tangible personal property which, pursuant to the contract of sale, is required to be shipped and is shipped to a point outside this state by the retailer by means of: (a) facilities operated by the retailer, or (b) delivery by the retailer to a carrier, customs broker or forwarding agent, whether hired by the purchaser or not, for shipment to such out-of-state point.
For purposes of this section, the term "carrier" shall mean a person or firm engaged in the business of transporting for compensation tangible personal property owned by other persons, and includes both common and contract carriers. The term "forwarding agent" shall mean a person or firm engaged in the business of preparing property for shipment or arranging for its shipment.
Ca. Rev. and Tax. Code § 6396