California Code, Government Code - GOV § 23290

The officers of the transferring county shall immediately execute and deliver to the board of supervisors of the accepting county, copies of all assessments or other proceedings relative to the assessment and collection of the current state and county taxes on property within the transferred territory.  The copies shall be filed with the respective officers of the accepting county who would have their custody if the proceedings had been originally had in that county and shall be deemed originals.  All proceedings recited in such copies shall be deemed original proceedings in the accepting county and have the same effect as if the proceedings had been had at the proper time and in the proper manner by the respective officials of that county.  The officials of the accepting county shall proceed with the assessment and collection of the taxes as if the proceedings originally had in the transferring county had been originally had in the accepting county.