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Portal to Porcupine Shuttle

An epic backcountry point-to-point ride crossing a mountain ridge.

Mountain Biking Severe

17 km
445 m
1 km
1-2 hrs
Low Point
1.9 km
High Point
2.8 km
Portal to Porcupine Shuttle Map

Portal to Porcupine is a big mountain point-to-point ride crossing a ridge from one side to the other. It easily ranks among the best backcountry rides near Big Sky, combining massive terrain, rowdy singletrack, and beautiful views.


Exactly how much of the climb you can shuttle and how much you have to pedal up depends on the vehicle you're driving. The road to the upper trailhead isn't dramatically technical, but it's just downright rough. The road grade is filled with smooth, embedded rocks that make for slow, bumpy driving. Most SUVs and crossovers will make it up just fine, as will high clearance 4x4 vehicles. Sedans are a no-go, smaller crossovers could have problems, and you might not want to brave the road if you're worried about rattling your vehicle to death.

Even if you can shuttle all the way to the top of the road, you'll still have to grind up another 1,200 vertical feet or so to reach the high point of the route. This provides plenty of time to warm up and get the blood flowing before you drop in to the gnarly descent.

The descent begins at an obvious pass over a mountain ridge and a sign that reads "Steep Grades Ahead." Indeed.

The trail begins twisting down the mountain, traversing over features that are merely rough, and not all that entertaining. During the climb, you'll undoubtedly have noticed the motoed out sections of singletrack, and this moto character persists into the descent. But after a mile or two, things start to look up: beautiful views open up through the trees, warranting a pause to soak up the grandeur of the endless Montana mountains. The singletrack begins to get more interesting as well, with the mere roughness transforming into a rowdy black diamond descent filled with rock gardens, boulders, roots, ledge drops, and more. A few sections even feel feature-filled as you skid down the occasional rock slab into a hairpin turn.

Lower down, the trail can get harder to follow. As of the time of this writing in 2021, quite a few large trees had fallen across the trail, and it appeared that nobody had bothered to clear the trees in a couple of years. Instead, the motos have just started bypassing around the downed trees, creating side trails and alternates which makes for difficult navigation in spots. At the bottom, the trail pops out into the Grizzly Loop/Porcupine Creek trail system, but the trail exit is grassy and unmarked. It feels odd, but it seems to be the Montana way.

At this junction, you can turn either left or right to get to the Porcupine Creek Trailhead, but this route as mapped takes a slightly longer jaunt down to the left, then follows the named Porcupine Creek trail as it undulates up and down (but mostly down) along the banks of the creek. These last few miles, while on a more mellow grade than the previous trail, still offer some delightful flowy, smooth turns as you whip through the wide-open meadows.

All in all, this is a rad ride that is worth putting on your Southern Montana to-do list!



Widely variable, narrow trail tread with steeper grades and unavoidable obstacles of 15in/38cm tall or less. Obstacles may include unavoidable bridges 24in/61cm wide or less, large rocks, gravel, difficult root sections, and more. Ideal for advanced-level riders.

Medium Exposure

2 out of 4

The trail contains some obstacles such as outcroppings and rock which could cause injury.


3 out of 4

Little chance of being seen or helped in case of an accident.

Best time to visit

between July and September


  • Technical
  • Shuttle-run
  • Singletrack
  • In the forest
  • Roots
  • Rock Rolls
  • Rock Gardens

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Guidebooks in this area