One of the most scenic hikes in Rocky Mountain National Park. Lots of views, lakes, creeks, wildflowers, etc. Challenging but not dangerous. Three return routes offer choices of about 17 miles, 20 miles, or 25 miles (total distance).
Start at the Wild Basin Ranger Station trailhead. This is off the Peak to Peak Highway (CO 7), just north of Allenspark, or a ways south of Estes Park. About an hour from Boulder.
From Wild Basin Ranger Station (40N12.517, 105W33.910, 8500 feet), go 1.5 miles towards Thunder Lake. Then take the cut-off trail (40N12.014, 105W35.292, 8902 feet) to the right (marked "Pine Ridge," "Tahosa," "Aspen Knoll," and "Siskin" campsites). This rejoins the main trail after 1.3 miles. Continue another 1.3 miles to the Lion Lake junction. This 4.1 mile section took us 55 minutes at an easy running pace. Take the Lion Lake trail 2.2 miles up to Lion Lake. Getting to the end of the trail (and timberline) from the trailhead is about 90 minutes.
From the head of Lion Lake, follow the cairns or the creek up past Trio Falls. Refill your water bottles here, it may be the last water for several hours. Stay to the left of Lion Lake #2 and Snowbank Lake. You'll see a hill to your left. Climb the hill but angle to the right of the summit. You'll then see an easy ridge going up to the Divide. Just walk up the ridge, enjoying the impressive views of Mount Alice's north face cliffs.
When you get to the Divide, the pass is called Hourglass Pass (12,500 feet). You could go north to Chiefs Head Peak (13,579 feet). To go up Mount Alice, head south as the Divide narrows to twenty feet or so. Scramble through the boulders up Mount Alice. The difficulty is similar to Longs Peak from the Boulderfield to the Keyhole. Some people get scared here but there's no danger, as the mountain is at least a hundred meters wide and the slope is at most thirty degrees. The only danger would be slipping on a snowfield and sliding off a cliff, so avoid the snowfields.
The hike from the end of the trail to the top of Mount Alice (13,310 feet) is about two miles, so, including a break to filter water, getting from the trailhead to the top of Mount Alice should be about three hours. Continue south along the tundra. The only danger here is lightning so watch the weather. Boulder-Grand Pass is just about a mile south of Mount Alice. It's the lowest point between Mount Alice and the Cleaver. You'll see Lake of Many Winds directly below you, and Thunder Lake beyond that. It's the shortest way back, but the top section is steep, loose talus and scares some people. A small trail starts at Lake of Many Winds and goes down to the main trail at Thunder Lake. You then have 5.5 miles back to the trailhead, for a total of about 17 miles.
For a more scenic, fun route, continue south on the Divide past Boulder-Grand Pass to the Cleaver. This is the next narrow part of the Divide. You'll see, to the west, Lake Verna, Spirit Lake, Fourth Lake, and Fifth Lake. Ahead is Isolation Peak, which you can't get to to directly without rock climbing. To the east you'll see Indigo Pond. The descent is steep, loose talus, but easier than Boulder-Grand Pass.
Indigo Pond is a beautiful spot to rest and refill water bottles. Continue down the valley to Eagle Lake. Take off your shoes and walk through the shallow, sandy head of Eagle Lake. On the south side of Eagle Lake you may have to put your shoes on again to walk through the lake as the bottom becomes rocky, or you can scramble through the krummholtz. Your goal is the hill south of Eagle Lake, above a large rock outcropping in the lake. On the top of the hill you'll see cairns marking a trail down to Box Lake. This small trail follows the creek draining Box Lake through meadows of wildflowers, then leaves the creek to enter the forest and follow around the base of Tanima Peak.
When the trail gets to North St. Vrain Creek (40N13.220, 105W38.456, 10490 ft; a boulder with a cairn), you could follow the trail up to Thunder Lake and join the main trail. Or you can save a mile and a half by taking a quarter-mile shortcut. Head on a NW compass bearing to get back on the main trail at 40N13.380, 105W38.429, 10500 feet. On the shortcut, don't cross any small creeks, rather follow them up the main trail. You then have less than five miles back to the trailhead. Total time is about nine hours.
For a longer day, you can also go up Isolation Peak. From Indigo Pond go down a quarter-mile, until you can climb up (south) around Eagle's Beak. You don't need to go all the way down to Eagle Lake. With some easy rock climbing you'll get to Frigid Lake, below Moomaw Glacier. Then it's an easy walk up Mahana Pass and to the summit of Isolation Peak (13,118 feet). From there you go down another steep, loose talus slope to Isolation Lake, then down to Pipit Lake, Lark Pond, Bluebird Lake and onto the main trail and 6.4 easy miles back to the trailhead. Total distance is about 25 miles or under 12 hours.
A trekking pole is helpful on the loose, steep talus.
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