Exploring Zion is a lesson in geology because you can see it happening; for example, witness the “spring lines,” areas where water seeps out of rock, create “hanging gar-dens.” Because sandstone is porous, water can percolate down through the rock until it’s stopped by a layer of harder rock. Then the water changes direction, moving horizontally to the rock face, where it seeps out, forming the “spring line” that provides nutrients to whatever seeds the wind delivers, which sprout into plants and flowers you can see clinging to the sides of cliffs.
The jaw-dropping wonder of Zion National Park is found simply in its rocks—their formation, uplifting, shifting, breaking, and eroding. Of Zion’s nine rock layers, the most important in creating the park’s colorful formations is Navajo sandstone—at up to 2,200 feet, the thickest rock layer in the park. This formation was created some 200 million years ago during the Jurassic period, when North America was hot and dry. Movements in the earth’s crust caused a shallow sea to rise up and cover sand dunes. Minerals from the water, including lime from the shells of sea creatures, glued sand particles together, eventually forming sandstone. Later crust movements caused the land to lift, draining away the sea but leaving rivers that gradually carved the relatively soft sandstone into the spectacular shapes seen today.
So where do the colors come from? Essentially, from plain old rust. Most of the rocks at Zion are stained by iron or hematite (iron oxide), either contained in the original stone or carried into the rocks by goundwater. Although iron often creates red and pink hues, seen on many of Zion’s sandstone faces, it can also result in shades of brown, yellow, black, and even green. Sometimes the iron seeps into the rock, coloring it through, but it can also stain just the surface, often in vertical streaks. Deposits of salt left by evaporating water frequently cause white streaks, and rocks are also colored by bac-teria that live on their surfaces. These bacteria ingest dust and expel iron, manganese, and other minerals, which stick to the rock and produce a shiny black, brown, or reddish surface called desert varnish.
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