SH-3's southern terminus is near Arrow Gulch Creek Bridge to the east of Spalding on US 12 on the Nez Perce Indian Reservation in Nez Perce County. It then heads generally northeast into eastern Latah County, where it leaves the reservation, and continues through Juliaetta and Kendrick, where it intersects SH-99. It then continues generally north to Deary, where it overlaps SH-8. The overlapping highways continue east and northeast to Bovill, where they diverge.
