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13.3 miles
Distance
2,249 ft
Climb
-2,255 ft
Descent
2 miles
High Point
-2 ft
Altitude change
6,382 ft
Altitude min
6,388 ft
Altitude start
6,388 ft
Altitude end
-26.5%
Grade max
32.3%
Grade min
6 miles
Distance climb
7 miles
Distance down
2,615 ft
Distance flat
The top of Thunderbolt Mountain offers one of the most outstanding 360-degree views in the Helena area. All of the surrounding mountain ranges are visible from the peak. The high elevation and thick timber make this trail one of the last in the region to shed snow, and drifts are common into late June. The first part of the trail to Cottonwood Lake is very popular with backcountry horsemen and horsewomen, so be alert, and make sure to park courteously, leaving room for horse trailers to turn around.
The trail to Cottonwood Lake is a moderate climb. From the lake, the trail climbs steeply to the top of Thunderbolt Mountain. The junction is at the north end of the lake; if you carry on farther than that you have missed it and are headed into the Little Blackfoot watershed. Near the top, the trail skirts the CDT and recommended wilderness areas where bikes are not allowed, so resist doing any further exploring on your bike.
This ride also offers opportunities for connections with Little Blackfoot Meadows and Larabee Gulch to the north.
Take the Bernice exit of I-90 (Exit 151) and follow the Boulder River Road (staying to the left). Stay on the Boulder River road to the Thunderbolt Creek road, which is directly opposite the Whitehouse Campground. The junction is a distinctive Y and is signed. The Thunderbolt Creek road ends at the trailhead.
Detailed Description
Thunderbolt Mountain is a 13 mile popular intermediate route located near Helena Montana. This mountain bike only route can be used one direction and has a hard overall physical rating. This route includes 3 trails. This route climbs 2,249 ft with a max elevation of 8,580 ft then descends -2,255 ft.
Trail Issues on Route
- Significant Issue / Amber: 1 trail (newest: Jun 25, 2026)
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Stats
-
Distance13 miles
-
Avg time2 hr 41 min
-
Altitude min6,382 ft
-
Altitude start6,388 ft
-
Altitude end6,388 ft
-
Climb2,249 ft
-
Descent-2,255 ft
-
Grade max-26.5%
-
Grade min32.3%
-
Distance climb6 miles
-
Distance down7 miles
-
Distance flat2,615 ft
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Trail Conditions
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MBG & contributors - #1487 - 6,398 views
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