It extends 11.185 miles (18.00 km) from U.S. Route 95 (US-95) east of Copeland, north to British Columbia Highway 21 (BC 21) in Porthill.

The route serves as a connector between Bonners Ferry, via US-95 south, Porthill, and Creston, BC.

[4][5] SH-1 runs 11.92 miles (19.18 km) from U.S. Route 95 (US-95) east of Copeland, north to BC 21 in Porthill.

[7][8] SH-1 was originally created in the 1920s as part of Sampson Trail B, which ran from Boise north to Lewiston, Coeur d'Alene, before entering British Columbia at Porthill.

[11] The loop became an Idaho Scenic byway on January 21, 2004, as the Wild Horse Trail.