Thunder Mountain (CO)

Page Type Page Type: Mountain/Rock
Location Lat/Lon: 40.48620°N / 105.8549°W
Activities Activities: Hiking, Mountaineering
Seasons Season: Spring, Summer, Fall, Winter
Additional Information Elevation: 12040 ft / 3670 m
Sign the Climber's Log


Thunder Mountain is at the northern end of the Never Summer Range and sits along the northwest border of Rocky Mountain National Park with the Colorado State Forest. As part of the Never Summer Range, the Continental Divide crosses over the peak. Thunder Mountain also serves as the point where three Colorado counties (Larimer, Grand, and Jackson) meet.

The north and west slopes of Thunder Mountain lie in the Colorado State Forest and the south and east slopes are in Rocky Mountain National Park. Generally Thunder Mountain is climbed as part of a loop including Lulu Mountain and Mount Neota, though numerous variations can be be completed with other points of interest such as the Michigan Lakes are in the area. There is some talus right at the summit, but nothing that cannot be easily avoided. In general, the slopes of Thunder Mountain are grassy slopes. The summit is marked with a moderate size cairn. The cairn is large enough to serve as a windbreak if necessary.

Thunder Mountain is not one of the more significant mountains with consideration to the other mountains in Rocky Mountain National Park, however it is over 12k feet. When I climbed it in 2006 there was no register at the top. Thunder Mountain and its neighbor, Lulu Mountain, provide phenomenal view points looking west towards the Michigan (American) Lakes and also Snow Lake, with Nohku Crags, Static Peak and Mount Richthofen serving as the backdrop to this majestic location.

Route Overviews

Three trailheads serve as access points for Thunder Mountain. La Poudre Pass and Colorado River trailhead serve as access points from Rocky Mountain National Park. Thunder Mountain can also be accessed from the American Lakes Trailhead on CO Route 14 in the Colorado State Forest. See Getting There below for directions to the trailheads. All Routes to Thunder Mountain involve off trail travel and thus are rated as Class 2. Generally this travel is straight forward though appropriate knowledge in the use of a compass and map is suggested.


From the gate at La Poudre Pass Ranger Station leave the road, heading generally west. The National Park boundry is marked in this area and can serve as a trail marker of sort though no established trail is available. After climbing through the woods, timberline will be reached. Continue climbing up the slopes (mainly grassy with a little talus) of Mount Neota. Mount Neota is mainly a bump along the southeast ridgeline from Thunder Mountain. The top of Mount Neota is reached around 1.4 miles from La Poudre Pass. From this point the directions are relatively straight forward. Continue hiking northwest along the ridgeline to the summit of Thunder Mountain (approximately 0.6 miles). For those wanting a more circitous route, you could head over to Thunder Pass and follow the trails back to La Poudre Pass. Paraphrased from Lisa Foster's RMNP: The Complete Hiking Guide.


Thunder Pass is accessed from a maintained trail (conveniently called the Thunder Pass Trail) from RMNP, and there is also a maintained trail that leads to Thunder Pass from the American (Michigan) Lakes in the Colorado State Forest. At the height of land, the two trails peter out on the grassy slopes of the pass. There are several visible signs that announce the national park boundy as well as a wooden trail sign identifying the location as Thunder Pass.

From this point there are two options to access Thunder Mountain. One can either climb the grassy slopes to the summit of Lulu Mountain or skirt cross country across the slopes of Lulu Mountain to the saddle separating the two mountains. Lulu Mountain is a nice mountain in its own right and provides a wonderful view point looking south along the Never Summer Range. Going cross country is not a particularly difficult task from this location as you are above the timberline and it is merely walking across rolling grasslands. (Taking this route provides some nice views of the various bands of rock that form Thunder Peak). Most of this traverse is completed with little elevation change, though there is a short, steep climb up to the saddle. From the saddle betwen Lulu and Thunder Mountains it is a steep climb of approximately 0.3 miles to the summit over grassy slopes. There is some minor talus near the summit, but nothing that should be considered worrisome.


Though a longer trek than the first two trailheads, access is also available from the State Forest. From the trailhead, follow the trail up to to the Michigan Lakes (about 5 miles with an elevation gain of approximately 1400 feet.) From there on can continue on the trail up to Thunder Pass and follow the one of the routes detailed above. For the slightly more adventerous, from the Michigan Lakes, head generally in an easterly direction across the rolling grass lands to the slopes of Lulu Mountain and continue cross country to the saddle between the two peaks.

There is probably a third option as well if Thunder Mountain is the sole objective of the day. Maps appear to suggest that trails in the Colorado State Forest parallel the drainage from the Michigan Lakes. There are no apprent large obstacles (or technical route finding necessary) from my various vantage points on a crossing of the outlet and climbing the slopes up to the saddle. Obvious caution should be given at times of high water. As it stands this would certainly require more exploration as a possible route. Anyone with more knowledge of the area feel free to offer suggestions.

Getting There....

La Poudre Pass: La Poudre Pass is legally accessable by car off of the Long Draw Road. Of course La Poudre Pass is also at the northern end of the Grad Ditch, but traffic is limited along this road to NPS and Grand Ditch Company personel. The Long Draw Road (FR 156) turns off of Colorado Route 14 east of the Joe Wright Resevoir. The trailhead is at the end of the road. There is a gate preventing continued access onto the Grand Ditch. Access via this trailhead may be limited in the winter months. Contact the local ranger district for road conditions.

Colorado River Trailhead: The trail head is located on the west side of US Route 34. It is approximately 11 miles north of Grand Lake and nearly 30 miles west of Estes Park. See the SP Colorado River Trailhead page created by Nelson for further details.

American Lakes Trailhead: The trailhead is located on the south side of Colorado Route 14. Look for the turn off on the left side of the road after crossing Cameron Pass. There are signs for Agnes and American Lakes. Note there is a fee (see RED TAPE). Bear to the left on the side roads and you will come to the trailhead parking area by the gate.

Andy has good local landmarks and mileagefor getting to thses trailheads on his SP page for Lulu Mountain.

When to Climb...

In general like most of Rocky Mountain National park, the summer (snow free) hiking season is between July and September. Although Thunder Mountain does not have as much elevation as some of the more notable peaks, there is not much concealment in the area. It is advisable to limit exposure before afternoon thunderstorms roll in.

Winter access is available from the Colorado State Forest leaving open the possibility of a winter ascent.


There are several camping options in the area in both Rocky Mountain National Park and the Colorado State Forest. Any camping that is done in Rocky Mountain National Park is at designated back country sites only and permits are required. Box Canyon is the closest back country campsite location to Thunder Mountain. (There are two sites at this location - you want the second one you come to after the Grand Ditch as it has a nice waterfall nearby).

The Colorado State Forest has several campgrounds. Camping permits are required for campground users. Backcountry camping is allowed around the American Lakes. However the website advised to contact a forest ranger first. No mention is made on the web site of permits, but the ranger will know for certain. For those where a tent is just a little to restrictive, there are yerts and cabins available for rent as well.

In all circumstances, Leave No Trace ethics should be followed.

Red Tape

Both Rocky Mountain National Park and the Colorado State Forest are fee use areas.

Entrance into RMNP is $20 for a 7 day pass. There are various other entry passes for sale. Fees are also in place for camping. See the NPS Rocky Mountain web site for further details on fees.

The Colorado State Forest has a daily use fee of $5. An annual pass is also available. See the Colorado State Forest web site for further fee details.