Highway 17
From Santa Cruz County history wiki
State Highway 17 (officially "California State Route 17") runs north from a junction with Highway 1 in Santa Cruz, through Scotts Valley, and on over the Santa Cruz Mountains to Los Gatos and San Jose in Santa Clara County.
Only one state highway originates elsewhere on both ends and passes through Santa Cruz County: Highway 1. Five highways originate in Santa Cruz County and pass out of it: Highway 9, Highway 17, Highway 35, Highway 129, Highway 152. One begins and ends within the county: Highway 236.