Zion National Park
** Location of Zion NP **
Zion ... immutable yet ever changing, the cliffs of Zion stand resolute, a glowing presence in late day, a wild calm. Melodies of waters soothe desert-parched ears, streams twinkle over stone, wren song cascades from red rock cliffs, and cottonwood leaves jitter on the breeze. But when lightning flashes water falls erupt from dry cliffs, and floods flash down waterless canyons exploding log jams, hurling boulders, croaking wild joyousness, and dancing stone and water and time. Zion is alive with movement, a river of life always here and always changing.
Everything in Zion takes life from the Virgin River's scarce desert waters. Water flows, and solid rock melts into cliffs and towers. Landscape changes as canyons deepen to create forested highlands and lowland deserts. A ribbon of green marks the river's course as diverse plants and animals take shelter and thrive in this canyon oasis. From the beginning people sought this place, this sanctuary in the desert's dry reaches. The very name Zion, a Hebrew word for refuge, evokes its significance.
Zion National Park is located along the edge of a region known as the Colorado Plateau. The rock layers have been uplifted, tilted, and eroded, forming a feature called the Grand Staircase, a series of colorful cliffs stretching between Bryce Canyon and the Grand Canyon. The bottom layer of rock at Bryce Canyon is the top layer at Zion, and the bottom layer at Zion is the top layer at the Grand Canyon.
Sedimentation ... Zion was a relatively flat basin near sea level 240 million years ago. As sands, gravels, and mud eroded from surrounding mountains, streams carried these materials into the basin and deposited them in layers. The sheer weight of these accumulated layers caused the basin to sink, so that the top surface always remained near sea level. As the land rose and fell and as the climate changed, the depositional environment fluctuated from shallow seas to coastal plains to a desert of massive windblown sand. This process of sedimentation continued until over 10,000 feet of material accumulated.
Lithification ... Mineral-laden waters slowly filtered through the compacted sediments. Iron oxide, calcium carbonate, and silica acted as cementing agents, and with pressure from overlying layers over long periods of time, transformed the deposits into stone. Ancient sea beds became limestone; mud and clay became mudstones and shale; and desert sand became sandstone. Each layer originated from a distinct source and so differs in thickness, mineral content, color, and eroded appearance.
Uplift ... in an area from Zion to the Rocky Mountains, forces deep within the earth started to push the surface up. This was not chaotic uplift, but very slow vertical hoisting of huge blocks of the crust. Zion’s elevation rose from near sea level to as high as 10,000 feet above sea level. Uplift is still occurring. In 1992 a magnitude 5.8 earthquake caused a landslide visible just outside the south entrance of the park in Springdale.
Erosion ... this uplift gave the streams greater cutting force in their descent to the sea. Zion’s location on the western edge of this uplift caused the streams to tumble off the plateau, flowing rapidly down a steep gradient. A fast-moving stream carries more sediment and larger boulders than a slow-moving river. These streams began eroding and cutting into the rock layers, forming deep and narrow canyons. Since the uplift began, the North Fork of the Virgin River has carried away several thousand feet of rock that once lay above the highest layers visible today.
Geology-in-Action ... flash floods occur when sudden thunderstorms dump water on exposed rock. With little soil to absorb the rain, water runs downhill, gathering volume as it goes. These floods often occur without warning and can increase water flow by over 100 times. In 1998 a flash flood increased the volume of the Virgin River from 200 cubic feet per second to 4,500 cubic feet per second, again damaging the scenic drive at the Sentinel Slide.
Source: Tourist site brochure, US Government Printing Office
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