In the Flathead National Forest, the Alpine Trail (#7 / 5000+) runs the length of the Swan Mountain Range from Columbia Mountain in the north to the Inspiration Pass in the south. The remote Alpine Trail runs the ridgeline about 60 miles ascending numerous peaks above 7000 . It is no doubt the most scenic trail in the FNF but is also the most rugged. After the 3000+ vertical ascent to the ridge, expect a narrow, brushy, rocky, rooty, dished-out trail through grissley, mountain lion and moose backcountry. DO NOT UNDERESTIMATE THE DIFFICULTY OF THIS TRAIL. Triple your time, water and food estimates. Double check the status of side trails shown on the Forest Service maps due to many recent closures. Many mountain bike riders have dreamed of a self-supported, multi-day trip down the length, but few if any have succeeded since panniers and trailers wont pass.
The southern trailhead starts at Napa Point off FS554 (near Swan State Forest Goat Creek ranger station) and follows the Napa Point Trail (#31/3.5mi.) up to Inspiration Pass. From there, the Alpine Trail runs north roughly 15 miles to Six Mile Mountain. A break in the trail requires a detour (via TR#74 north -> FS5345 north -> FS381 northwest -> TR#72 west).
Back on the Alpine Trail, it continues north a couple more miles until a detour is required around the Jewel Basin Hiking Area (via Echo Broken Leg Trail (#544/11mi.) northwest -> FS5392 west -> north on first main road -> FS5390 northeast -> Strawberry Lake Trail (#5/3mi) east).
The final stretch on the Alpine Trail runs from Strawberry lake about 15 miles north to Columbia Mountain -- this is the most difficult stretch. From here, its down via the Columbia Mountain Trail (#51) northwest into Columbia Falls. Again, DO NOT UNDERESTIMATE THE DIFFICULTY OF THIS TRAIL.
Overall, Alpine Trail is the 3rd most popular mountain bike trail of all 32 mountain biking rides in Montana.