|Getting There:||Located inside Rocky Mountain National Park, access to Chasm Lake is accessed from the Longs Peak Trailhead about 45 miles northwest of Boulder. Take U.S. 36 north to Lyons, then head west on Colo. Highway 7 through Allenspark and north toward Estes Park. Turn left onto Longs Peak Road about a half mile to the Longs Peak Trailhead and parking lot on the left. Due to the popularity trailhead for Longs Peak hikers and climbers, parking is always a challenge on Fridays, Saturday and Sundays and often fills up before 5 a.m. If you can be flexible with your schedule, it's much less crowded from Mondays through Thursdays.|
Chasm Lake is a stunning high-alpine lake just below Longs Peak inside Rocky Mountain National Park and the 8.2-mile out-and-back roundtrip trail run to this remote gem can be a summertime treat. The route starts from the Longs Peak Trailhead (elevation 9,450 feet) as a dirt idyllic singletrack trail that climbs through a thick forest of lodgepole pine, spruce and fir, then continues ascending as it emerges above treeline and continues along rocky, subalpine terrain to a fork in a trail. The route to the right heads toward the Keyhole Route on the way to Longs Peak, while the trail to the left heads toward Chasm Lake.
The final mile or so to the lake descends into an alpine basin with 13,911-foot Mt. Meeker looming in the distance, then passes over the top of Columbine Falls before climbing again as it approaches a massive rock face adjacent to the lake. A short, moderately steep hike up a final section of rocky terrain leads to the lake at 11,700 feet. Chasm Lake sits in a deep cirque at the base of Mount Lady Washington (13,281 feet) toward the north and Longs Peak (14,259 feet) further to the the west.
The route is entirely runnable for experienced trail runners, but it can be challenging because of some steep sections of trail, the high altitude, exposure to sun and wind and potential for frequent afternoon thunderstorms in the summer. The terrain is a combination of dirt, gravel and rock, so wearing durable trail running shoes is a must. Carry ample water, energy snacks and a rain shell and be sure to wear sunblock.