Protected within Zion National Park's 229 square miles is a spectacular cliff-and-canyon landscape and wilderness full of the unexpected, including the world's largest arch -- Kolob Arch -- with a span that measures 310 feet. Marking the western edge of the Colorado Plateau, Zion National Park is a lovely concatenation of colorful rock layers sliced into steep-walled canyons by some 15 million years of uplift and erosion by the Virgin River and its tributaries.
The most striking layer is the reddish Navajo sandstone, whose smooth, sheer cliffs rise to over 2,000 feet at some points. Navajo sandstone is characterized by broad, sweeping cross-beds that originally formed in desert sand dunes that covered the region from 135 to 190 million years ago. Cross-beds --layers of sedimentary rock inclined at angles of up to 35 degrees from horizontal -- form from deposits of sand on the steep, down-current side (lee slope) of a sand dune. The slope of the cross-beds tells geologists the direction of prevailing winds at the time of dune formation; different directions of cross-bedding indicate changes in wind direction.
Normally a small stream, the Virgin River can flood following storms; some of its side drainages end in high "hanging valleys" that send spectacular waterfalls into the river gorge when runoff occurs. Drivers can view the Virgin River canyon from Zion Canyon Scenic Drive, while hikers take established trails or seek more difficult unmarked routes through washes and canyons. The Narrows, where visitors are dwarfed by 2,000- to 3,000-foot cliffs, and the parallel "finger canyons" of the Kolob Terrace in the northwestern corner of the 146,560-acre park are popular destinations.
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