Rev. & Tax. Code, § 6247

(a) On and after the effective date of this section, it shall be presumed that tangible personal property delivered outside this state to a purchaser known by the retailer to be a resident of this state, as defined in Section 6248, was purchased from a retailer for storage, use, or other consumption in this state and stored, used, or otherwise consumed in this state.

(b) This presumption may be controverted by a written statement, signed by the purchaser or their 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 California Department of Tax and Fee Administration that the property was not purchased for storage, use, or other consumption in this state.