Thunder Lake Trail is a 11.5 mile moderately trafficked out and back trail located near Allenspark, Colorado that features a lake and is rated as difficult. The trail offers a number of activity options and is accessible from March until October. Horses are also able to use this trail.
This is a really long one (at least for me) but it wasn't super difficult. The elevation gain is mostly gradual and there's several cool things to see along the way. I started at 8:30 and got back to the trailhead at 2:00, so it'll take a good chunk of the day to do, but really great mountain and lake views at the end. I think Sky Pond, Mills, Haiyaha, and Emerald lakes have a better view at the end for less effort, but I'm glad I did this one; it was fun.
SO BEAUTIFUL, the trail is very long and ALL up hill on the way to the lake but once you're there, it's worth it. The lake is surrounded by big mountains and its not crowded due to its difficulty to reach. Good place for lunch. The walk there was very scenic, lots of pines and then sections with different things to see and flowers. You cross 2 amazing waterfalls also. Way back is easy, all down hill
This hike is NOT hard! And boring? What?! From the trailhead, there's Coleman Falls, Calypso Cascades, and Ouzel Falls. There is a break here until Thunder Lake is reached, but along the way are fascinating things if you stop to look. Through the trees, peaks pop into view. The St. Vrain is your constant companion, dipping under bridges and gurgling alongside. Meadows break out where deer and moose wander. Interesting boulders form instant shelter from rain. Never a dull moment. It wasn't very crowded after Ouzel Falls. Take the side trail to the top of Ouzel Falls. It's well worth it. All six of us agreed this one is easy with moderate on occasion. Fantastic, but long, hike!
I have done this trail as a day hike and backpacking. I love it as a day hike. It's a pretty easy overnight backpacking trip--exceptional for outta town friends who may not be acclimated to the altitude. The forests are beautiful the last 2 or so miles towards Thunder Lake. Typically a lot of traffic. I enjoyed it.
This was my third time to Wild Basin- one failed attempt at Sandbeach Lake due to snow, and one failed trip to Ouzel Lake due to the bridge being out since May, 2013 (we just went to Ouzel Falls instead).
Thunder Lake itself is a rewarding destination, framed by Tanima Peak and Boulder-Grand Pass (which does offer dramatic views, as another reviewer said!). The backdrop of the mountain is so close and abrupt that it kind of surprised me! Pictures do not do it justice. Wildflowers dotted the landscape all the way to the west side of the lake, along the trail. While I am so happy to have hiked here, the reason for the three stars is that it was... kind of boring to get to.
The St. Vrain creek was so enjoyable to walk next to, and the valley was pretty, but you are mostly in the trees, especially once you get to the primitive campsite spur trail. However, besides the length, I didn't find the trail to Thunder Lake to be too strenuous. Yes, there were some switchbacks, but not many, and there were many flat parts of the trail for resting.
Again, I did very much enjoy this trail, and do not at all regret hiking it, but compared to other trails I have hiked, I gave it three stars. I would like to come back to this area in a few weeks when the aspen turn yellow.
It's about 6.8 miles one way, about 2100' in elevation gain, with most of the gain in the second half of the hike. Difficult hike with a full pack (or without a pack), but plenty of points of interest along the way to use as rest stops.
The first half or so is on the Ouzel Lake trail, with the St Vrain river rushing next to the trail. Calypso Cascades runs underneath one of the many bridges on the trail. Ouzel Falls is a very short side hike off the main trail. The second half of the hike is all uphill on a very rocky trail.
Lake is tucked up against a mountain, making for dramatic views. The cascading river feeding the lake is on the far side.
Backcountry camp sites are about 200 yards above the lake, and require a permit and bear resistant container.