My Favorite Zion Canyon.
Oh my heck, it has everything – a rough-tough smackdown approach; a verdant, wooded canyon with spectacular soaring walls; multiple rappels through intimate, sculpted narrows; some walking in the hot sun; a monstrous rockfall that creates a seasonal lake; a big rappel into a pool; wading pools in a jungle paradise; and finally a slippery slab rappel to the whirring camcorders of numerous tourists. Not too long, not too short - Mystery is a great outing.
Though information is sketchy, Mystery was first descended in the 1960s. Numerous "interesting" anchors attest to the improvisatory skills of early descentionists, including chunks of rebar pounded into drilled holes. Anchors in Mystery are generally fixed, though judgment is required to figure out which of the antique anchors to use. An interesting feature of the canyon is a giant sand pile created by a landslide in the early 70's – a 400-foot pile of rock and sand that dams the canyon and creates a "Devil's Hole". On occasion, the lake before the slide is up to 10 feet deep and provides a long and stimulating swim. Most of the time it is dry or a boggy gumbo. This small "lake" is similar to larger lakes that had a profound effect on Zion's topography in the geologically recent past.
Mystery can be approached from either the Weeping Rock shuttle stop in the main canyon or from the East Mesa trailhead on the Zion Ponderosa Ranch. The second option saves you 2100 feet (640m) of climbing on a steep trail, but requires a car shuttle. Mystery is a popular canyon, and permits can be hard to get. Expect to share the canyon with other parties, especially on weekends.