The International Selkirk Loop begins on U.S. Route 2 at the Washington-Idaho state line, in the city ofNewport. The highway proceeds west for a short distance, passing several buildings that make up the twin, before U.S. Route 2 splits off, and the Loop designation transfers to Washington State Route 20. The highway proceeds northwest, traveling parallel to the Pend Oreille River. The road continues, intersecting several small roads before entering the community of Usk and intersecting Washington State Route 211. The roadway bends northward, passing the community of Cusick, and continuing parallel to the Pend Oreille. Continuing northward, the highway intersects several small roads, and makes a large northeastward bend, before returning to traveling northward. It proceeds north, passing through a small portion of Colville National Forest, before entering Ione. While traveling through Ione, WA 20 splits off, and the Loop designation transfers to Washington State Route 31. Continuing northward, the roadway passes the Ione Municipal Airport, proceeding parallel to the Pend Oreille River, before crossing over the river and entering Colville National Forest. The road proceeds north, intersecting several small forest roads, before reaching the Canada–US border, where the WA 31 designation ends. The loop enters Canada, and the designation transfers to British Columbia Highway 6.
British Columbia
After entering British Columbia, the Loop proceeds northward, traveling parallel to a small creek. After intersecting several smaller roads, BC 6 intersects British Columbia Highway 3, which runs concurrently with the highway. The highway proceeds north, continuing along the course of the small creek, intersecting several small roads. After several miles, BC 3 splits off the highway. The route proceeds through the community of Salmo, before proceeding northeast. The road bends northwestward, before zigzagging along a valley floor. The roadway passes to the west of West Arm Provincial Park, and enters the community of Nelson. In Nelson, the Loop's designation transfers to British Columbia Highway 3A at a trumpet interchange. The road passes northeast through Nelson, before passing over an arm of the Kootenay Lake, and traveling eastward along the arm of the lake. The Loop designation transfers to the Kootenay Lake Ferry at the intersection of BC 3A and BC 31. The ferry is approximately in length, and connects the loop to the eastern shore of the lake. After crossing the lake, BC 3A continues eastward, passing several small buildings. The road passes through Crawford Bay, before bending south and traveling along one of the arms of the lake. While traveling along the lakeshore, the highway passes through the community of Gray Creek, and passes west of Lockhart Creek Provincial Park. The roadway passes along Duck lake, before intersecting several small roads. The road enters Creston, where the Loop's designation transfers to British Columbia Highway 21. The highway continues south, through Creston, passing numerous buildings which make up a portion of the community. The highway proceeds southward, running parallel to a large river, continuing to the Canada–US border, where the BC 21 designation terminates. The Loop reenters the United States, and the designation transfers to Idaho State Highway 1.
Idaho
The highway proceeds southeast, through the community of Porthill, before bending slightly northeastward. The road bends back southeast, and proceeds through rural area, before reaching an intersection with U.S. Route 95. The road proceeds southward, through rural area, occasionally intersecting a small road. After continuing southward, the highway intersects U.S. Route 2, which continues concurrently with the highway. The road proceeds south, crossing over the Kootenai River, before entering the community of Bonners Ferry. The roadway continues southeast, intersecting several small roads, and passing several buildings. The route proceeds southeast, intersecting several small roads, and passing west of the Kaniksu National Forest. The road proceeds south, entering the community of Sandpoint, and reaching an interchange with Idaho State Highway 200, where U.S. Route 95 splits off from the highway. The roadway continues westward, traveling parallel to the Pend Oreille River, and intersecting the occasional small road. It enters the community of Priest River, and passes the Priest River Municipal Airport. The highway intersects Idaho State Highway 57, before continuing west out of the town. The highway continues eastward, crossing over the Pend Oreille River, and reaching the Washington-Idaho state line, where the Loop begins again.
