Grains of sand were once driven bouncing across the desert by the wind, only to be caught within the steep face of a dune, where they became buried. Over time, with the aid of water and pressure, a cement of lime tied grain to grain and created a stone of sand, called the "Navajo Sandstone."
Today, however, the Virgin River is cutting Zion Canyon through that solid layer of resistant Navajo Sandstone. As it does so, the walls of the canyon relax and expand ever so slightly toward this opening, which causes cracks to form that run parallel to the canyon about fifteen to thirty feet inside its mighty walls.
The layers of siltstone and sandstone that lie directly beneath the Navajo Sandstone are softer and more easily eroded than the Navajo Sandstone itself. Thus, as the walls of Navajo Sandstone are undermined by the erosion of this softer material, water from rain and snow seeps into the cracks, where it freezes in winter, wedging them ever farther apart.
In addition to freezing, the water dissolves the cement, one drop of rain, one melting flake of snow at a time. The structure gradually weakens. For an instant in eternity, a single grain of sand--the last grain--holds in place the undermined wall. Then the grain moves…. The massive piece of rock falls, breaking away along the line of least resistance, leaving the graceful sweep of a huge arch sculpted in the face of the cliff a thousand feet above the floor of the canyon. And so is revealed yet another vertical face previously hidden as a crack inside the wall.
Below, the rock, shattered by the fall, gradually returns to free grains of sand that are once again blown hither and yon by the wind or carried toward the sea by the restless Virgin River. And who knows, that last grain of sand may be captured in another dune along the way to once again help create a mountain somewhere in the distant reach of time.
© chris maser 2002 All rights reserved.