SR 129 does not cross into Santa Clara County but the road comes within 700–900 feet of the Santa Cruz-San Clara County line.

Heading eastward out of town, SR 129 roughly parallels the Pajaro River along the Santa Cruz-San Benito County line before entering San Benito County near Chittenden.

Crossing the Pajaro River near River Oaks, the road runs southeast along Chittenden road to end at U.S. Route 101.

[4] Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage.

[1] Segments that remain unconstructed or have been relinquished to local control may be omitted.