Cal. Rev. & Tax. Code § 6247

On and after the effective date of this section, it shall be further presumed that tangible personal property delivered outside this State to a purchaser known by the retailer to be a resident of this State was purchased from a retailer for storage, use or other consumption in this State and stored, used or otherwise consumed in this State.

This presumption may be controverted by a statement in writing, signed by the purchaser or his authorized representative, and retained by the vendor, that the property was purchased for use at a designated point or points outside this State. This presumption may also be controverted by other evidence satisfactory to the board that the property was not purchased for storage, use, or other consumption in this State.