California Code, Streets and Highways Code - SHC § 2121

(a) In May of each year each county shall submit to the department any additions or exclusions from its mileage of maintained county highways, specifying the termini and mileage of each route added or excluded from its county maintained roads.  The department shall either approve or disapprove each inclusion or exclusion.  A county may appeal any disapproval as provided in Section 74.  The department shall certify county mileage figures to the Controller, as required.  No appeal shall affect any apportionment made by the Controller pending the determination of the appeal.  If, on appeal, additional mileage is allowed the county, the department shall immediately certify the corrected figure to the Controller, and the same shall be used for subsequent apportionments.

(b) Upon relinquishing any state highway or portion thereof to a county, the department shall immediately certify to the Controller the mileage so relinquished and the same shall immediately be added to the county's maintained mileage of county roads for purposes of subsequent apportionments.