Aspen, CO: Four Pass Loop

Four 12,000-foot passes, classic alpine views and a rugged loop around Colorado's most-photographed peaks make this 26.5-mile backpack a Rocky Mountain epic.

From the shores of Maroon Lake, this lollipop-loop climbs to Crater Lake and turns south for a clockwise loop around the Maroon Bells. Campsites, creek crossings, and cross-valley views pepper the 6.25-mile climb to pass number one: 12,500-foot West Maroon. The rocky saddle falls westward into Halsey Basin where there are several wildflower-festooned trails that lead to Crested Butte. This route turns north, hugging the basin’s eastern edge before climbing a steep, loose path toward pass number two: 12,415-foot Frigid Air. Long sweeping switchbacks descend eastward into Fravert Basin. After a wet river crossing of the North Fork Crystal River, the trail turns uphill for a tough, aspen-lined climb toward an alpine lake below pass number three: 12,400-foot Trailrider. Snowmass Peak looms overhead as the trail skirts scree fields and dips below treeline near Snowmass Lake at mile 18.

The final climb to pass number four: 12,462-foot Buckskin Pass winds 3.5 miles through wetland meadows and turns increasingly uphill near the pass. The last several miles of this loop switchback downhill crossing avalanche-battered hillsides and touching the edge of the Minehaha Gulch before closing the loop at Crater Lake where you'll retrace your steps the final 1.6 miles to the trailhead.

-Mapped by Kristy Holland and Anne Whetzel

Trail Facts

  • Distance: 41.9



Location: 39.0996513, -106.9376678

The trailhead parking lot is equipped with toilets and drinking fountains. Though there are three lots, they may fill on peak weekends and even overnight visitors might have to take the shuttle bus from the Aspen Highlands Village at the base of Maroon Creek Road.


Location: 39.0985336, -106.9408264

Follow Crater Lake Trail signs through the parking area and along the north shore of Maroon Lake. Be sure to stop for photos at this picturesque spot.


Location: 39.0980911, -106.9460297

Turn right at the signed Y-junction, and head uphill toward Crater Lake.


Location: 39.0971222, -106.9478378

The trail crosses two plank bridges just before a self-registration kiosk at the wilderness area boundary. Overnight hikers are required to fill out the free registration tag and leave detailed plans.


Location: 39.0914421, -106.9583282

The trail opens up after a few short switchbacks and begins a level, 0.3-mile wind through lichen-covered piles of angular rock. Up ahead you'll catch a glimpse of Crater Lake's muddy waters on the left.


Location: 39.0886536, -106.9659576

Turn left at this trail junction to follow the West Maroon Trail #1970. If you had a late start from the trailhead, you may choose to stop for the night at one of several Crater Lake campsites (site 6 is a favorite). If you're prepared for a longer hike, continue left up the valley toward West Maroon Pass.


Location: 39.0842896, -106.9698944

A split-log bridge precedes this ponderosa-shaded clearing. Pass left-hand spur trails to Crater Lake's Campsites 7-9 and 10-11 up ahead.


Location: 39.0788879, -106.9717865

The trail winds atop a rockfall and scree field. Northern views of Crater Lake are a little distracting, but the well-trod trail is easy to follow.


Location: 39.065048, -106.9719028

Water levels may be low in late summer, but this first substantial river crossing at mile 3.5 might be a snowmelt-swollen challenge in early summer. On the river's east side, a rocky clearing is a good spot to stop and have a snack and wring out your socks.


Location: 39.055191, -106.9768982

Several user-created trails merge on the opposite side of this 10-foot stream crossing. In late summer you may be able to stay dry, but expect to get wet when the river is swollen in early spring.


Location: 39.0424862, -106.9863653

There are no designated campsites above Crater Lake, but camping is allowed. Use established sites (there are 2-3 sites around the edges of this meadow) to reduce impact along this heavily-used trail.


Location: 39.0364189, -106.997261

After rolling uphill and across some easy stream crossings, the climb intensifies as the vegetation and air thins near the pass. Alpine meadows and flowers give way to red-tinted rocks for the final few hundred feet of climbing.


Location: 39.0357323, -106.9973068

West Maroon Pass, a 12,480-foot shoulder between Mount Bellview to the south and Belleview Mountain to the north, offers spectacular views of the valleys on either side.


Location: 39.0382791, -107.0087022

Turn right at this signed Y-junction toward Frigid Air Pass. The trail climbs gently to the northwest.


Location: 39.0427253, -107.0108054

There are no adequate campsites on this steep, hillside. Plan to spend your first night on the east side of West Maroon Pass, or allow plenty of time for a very long day one (over Frigid Air into Fravert Basin).


Location: 39.0521943, -107.0237788

Turn right at the signed 3-way junction. You'll traverse a grassy bowl beneath Frigid Air Pass before turning sharply uphill.


Location: 39.0538465, -107.0203979

This short, but very steep and loose 400 foot climb ends at the 12,415-foot pass. Welcome views of the Fravert Basin's grassy expanse and the Maroon Bells' rugged backsides await.


Location: 39.06726, -107.0160066

The trail drops through shrubby alpine meadows and enters the woods for the first time in 5 miles. As the trail enters the woods it passes a few small, slanted campsites.


Location: 39.0776168, -107.019029

The trail crosses several drainages as it winds down the basin's upper half.


Location: 39.0814622, -107.0255868

This shady campsite is large enough for several tents, but within a few hundred yards along the trail there are other, smaller sites as well.


Location: 39.0813441, -107.0279623

This ledge offers spectacular views into the basin's lower half. You'll catch glimpses of a waterfall on your right before the trail turns sharply downhill over several switchbacks.


Location: 39.0824893, -107.0413291

A Halsey Basin trail and westbound user trails merge at an unmarked junction in a clearing near a large, fallen tree. Continue straight toward the next junction before turning right, or turn right here to follow the faint user-trail toward the river.


Location: 39.0826069, -107.0422441

This ponderosa-shaded campsite sits near a creek and is less than 150 yards away from the North Fork Crystal River crossing.


Location: 39.0837476, -107.0419754

The trail's most substantial river crossing is a wet 20-foot wade across the North Fork Crystal River at mile 11. Brush up on creek-crossing safety tips and consider bringing trekking poles for this section of the trip.


Location: 39.0885115, -107.0557403

Turn right at the Y-junction toward Trailrider Pass. The next 1.5 miles zigzag up a steep, aspen-dotted hillside.


Location: 39.0969326, -107.0624638

Turn right at this Y-junction and continue following signs north and east toward Trail Rider Pass. Another set of trails leads west toward Geneva Lake.


Location: 39.0985663, -107.0522178

There is a small lake, a few lumpy campsites, and a small stream in this alpine valley below Trail Rider Pass.


Location: 39.1050865, -107.0490403

A few short, steep switchbacks top out at 12,400-foot Trail Rider Pass. Snowmass Peak looms to the north and the trail shoots left and switchbacks downhill toward Snowmass Lake.


Location: 39.1132115, -107.0341626

On a steep hillside just above Snowmass Lake, the trail winds around and across several scree fields. You'll have to rock hop on a few short sections of trail.


Location: 39.1166749, -107.0283598

Continue straight at this 3-way junction to continue toward Buckskin Pass, but turn left for a 10-minute detour to an open picnic-worthy clearing near the lakeshore.


Location: 39.1174316, -107.0301056

This clearing offers great views of Snowmass Mountain looming above the lake's western shore. There are several campsites in the forest just east of here.


Location: 39.1171722, -107.0263596

Go straight at 3-way junction to continue toward Buckskin Pass. Or, turn left to scope out several individual campsites and a larger group site, too.


Location: 39.1089668, -107.016304

This rocky outcropping hides another campsite, just 100 feet to the left of the trail. Sites like this one, away from the lake, are likely to be less crowded during peak summer weekends.


Location: 39.1074791, -107.008934

After passing beneath a red-hued rock face, the trail traverses a meadow over a series of steep, loose, rocky switchbacks.


Location: 39.1059532, -107.0041351

The trail crisscrosses Snowmass Creek near the east side of this marshy wetland area. The trail turns uphill for its final pass-bound climb.


Location: 39.1020164, -106.9925461

At mile 21.5 the trail hits 12,462-foot Buskskin Pass before turning downhill toward the trailhead (the route's high point). Snowmass Mountain dominates the western view and grassy slopes nearby offer dramatic contrast. Watch for mountain goats that frequent the rocky outcroppings above the pass.


Location: 39.1002541, -106.9849701

Go straight at the 3-way junction continuing downhill and bypassing the Willow Pass and Willow Lake Trail.


Location: 39.093544, -106.9785995

A shallow 20-foot stream crossing here may present trouble when water levels are high, but a wide section of relatively flat, pine-covered trail crosses several small streams up ahead.


Location: 39.090641, -106.9779053

Stop at this rocky outcropping for a peek into Minnehaha Gulch. Be careful near the cliff edge, the log-jammed river is about 100 feet below the rocky cliff.


Location: 39.0890198, -106.9695587

A stretch of broken aspen are evidence of this area's winter avalanche danger.


Location: 39.0886536, -106.9659576

Continue straight at this 3-way junction to close this route's 23-mile loop. It's an easy, rolling 1.7 miles downhill toward the trailhead.

Fravert Basin

Location: 39.083472, -107.0416993

Looking back toward Fravert Basin at a riverside junction just before the North Fork Crystal River crossing. © Kristy Holland

Trailhead Bus Stop

Location: 39.0984942, -106.9402742

A shuttle service stops at the trailhead and maybe the access only option for peak-season hikers. © Kristy Holland

Maroon Bells

Location: 39.0982277, -106.9420767

A view of the Maroon Bells from the trailhead. © Anne Whetzel

Rocky Trail

Location: 39.0916996, -106.9574833

Just over a mile from the trailhead, the trail flattens and winds through an angular scree field. © Kristy Holland

Trail #1970

Location: 39.088502, -106.9661093

West Maroon Trail #1970 turns south toward Crater Lake. © Kristy Holland

Stream Crossing

Location: 39.0651146, -106.971302

Even though this late-summer stream crossing is dry and easy, use caution on slick rocks. © Kristy Holland


Location: 39.0451194, -106.9854212

Summer wildflowers decorate already spectacular views of the 13,000-foot bowl above West Maroon Creek. © Kristy Holland


Location: 39.0424529, -106.9861078

A picturesque campsite below West Maroon Pass. © Anne Whetzel

Pass Climb

Location: 39.036853, -106.9973087

A hiker climbs the rocky, open trail toward West Maroon Pass. © Kristy Holland

Trail Sign

Location: 39.038253, -107.0087457

The Four Pass Loop trail can be faint, but its entire length is well-signed. © Kristy Holland

Basin Views

Location: 39.0812067, -107.0278001

A northwest view of the North Fork Crystal River's basin near mile 11.6. © Kristy Holland


Location: 39.0903589, -107.0575351

The hillside path toward Trailrider Pass switchbacks through small groves of aspen. © Kristy Holland

Heading North

Location: 39.0461193, -107.0154619

Hugging the flower-festooned alpine hillside between West Maroon and Frigid Air passes. © Kristy Holland

Frigid Air

Location: 39.0521183, -107.0239592

Frigid Air Pass is just a short, steep climb above this trail sign at mile 8.5. © Kristy Holland

Fravert Basin

Location: 39.0537847, -107.0200968

A view of the Fravert Basin from Frigid Air Pass. © Kristy Holland

Below Trail Rider

Location: 39.1002177, -107.0497137

The valley and alpine lake on the west side of Trail Rider Pass. © Kristy Holland

Trail Rider View

Location: 39.104955, -107.0489788

The southwestern view from Trail Rider Pass. © Anne Whetzel

Trail Rider Pass

Location: 39.1050216, -107.0489359

The view of Snowmass Lake from Trail Rider Pass. © Kristy Holland

Snowmass Descent

Location: 39.1140459, -107.0338511

You'll catch plenty of views of Snowmass Lake as the trail descends from Trail Rider Pass. © Kristy Holland


Location: 39.1140126, -107.0337224

As the trail drops toward Snowmass Lake, it winds around and across large-boulder scree fields. © Kristy Holland


Location: 39.099027, -106.9845629

If you need a mid-downhill rest, stop at this trail-side cascade. It's just below treeline and has a few flat-topped rocks perfect for sitting on. © Kristy Holland