NC 603: was born in 1931. It ran from its parent NC 60 (now Old US 421 SR 1233) Sugar Grove west to the Tennessee State Line (where it continued as an unnumbered road to Johnson City). Very quickly, the parent NC 60 was dissolved by US 321, then US 421.
NC 603 remained until 1961, when US 321 was re-extended west of Boone over it.

NC 603

NC 603 becomes US 321