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Routes in Sister Slab

Middle Way, The T 5.4 4a 12 IV 10 VD 3c


Sister Slab is an otherwise unnamed, large, granite slab approximately 0.3 miles south of Twin Sisters Peak in Boulder County, Colorado. The slab is located on public land managed by the Roosevelt National Forest and is accessible via the Twin Sisters Peak trail. The trail head for that trail is located on County Road 68J, along a stretch suited to mountain bikes and Jeeps. The slab is remote, undeveloped, and quiet.

The bulk of the slab is roughly 550 feet wide and roughly 370 feet tall at its tallest point. The slab ranges from low-angle to near-vertical and has a few large, overhanging roofs. The aspect is generally SSW.

The rock is sticky, medium-grained granite. The rock quality varies from weathered and smooth, to broken and blocky. There appear to be some sweet spots, where the slab is not too continuously smooth or broken up, where occasional protection can be placed in cracks, under flakes, and in pockets.

If you look hard enough, you find mention of people exploring the slab, the nearby Twin Sisters, and the neighboring boulders on public land. However, not much has been documented. There are several other rock features in the area that look interesting, but many, such as those around Forsythe Rock, are on private land. Please respect the privacy of the folks who live here.

Camping is officially allowed within a few miles of the slab, for example, at designated campsites along Winiger Ridge. Camping on the side of the road in undesignated locations could result in a visit from the county sheriff, especially if there is fire involved.

Getting There

Getting there involves three distinct phases: Phase 1, the driving part, takes between 30 (Flagstaff Road) and 40 (Magnolia Road) minutes from downtown Boulder. For the Flagstaff option, take Flagstaff Road west out of Boulder for about 8 miles until you reach Gross Dam Road. Park at the public parking area. For the Magnolia option, take Magnolia Road west for about 6 miles. Take a left and go SE on County Road 68J for about 2 miles and park at the public parking area for Forsythe Canyon and Winiger Ridge.

Phase 2 is probably best accomplished on a mountain bike, unless you have a monster truck. From the parking lot at Gross Dam Road, head east on Lakeshore Drive (paved road), which turns into 68J (rapidly deteriorating dirt road), for about 2 miles until you see the Twin Sisters Peak trail head on your right. If coming from the Winiger Ridge parking area on 68J, travel about 1.5 miles further on rapidly deteriorating 68J until you see the trail head on your left.

Phase 3 is a 20 minute hike up the Twin Sisters Peak trail. When you reach the first saddle, head west about 100 yards to the top of the slab. One way to the bottom of the slab is along the south edge of the slab. Don't stray too far from the base of the slab or you'll end up on private property.

In total, getting there from Boulder takes about 1.5 to 2 hours - 30 plus minutes in a car, 30 plus minutes on a bike, and 30 minutes on foot.

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Tim Meehan
Boulder, CO
Tim Meehan   Boulder, CO
Not much documentation for this climbing area. Here are a few threads to follow.……… Apr 12, 2017

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