Zion National Park, Utah
The very name Zion, a Hebrew word for refuge, evokes its significance.
(*Text not original content and is simply copied & compiled from NPS.gov*)
Zion National Park – Zion is Utah’s oldest national park, designated in 1919, and is located along the edge of a region known as the Colorado Plateau, encompassing some of the most scenic canyon country in the United States. Within its 229 square miles are high plateaus, a maze of narrow, deep, sandstone canyons, and the Virgin River and its tributaries. Zion also has 2,000-foot Navajo Sandstone cliffs, pine- and juniper-clad slopes, and seeps, springs, and waterfalls supporting lush and colorful hanging gardens. 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.
With an elevation change of about 5,000 feet-from the highest point at Horse Ranch Mountain (at 8,726 feet) to the lowest point at Coal Pits Wash (at 3,666 feet), Zion’s diverse topography leads to a diversity of habitats and species. Desert, riparian (river bank), pinyon-juniper, and conifer woodland communities all contribute to Zion’s diversity. Neighboring ecosystems-the Mojave Desert, the Great Basin, and the Rocky Mountains-are also contributors to Zion’s abundance.
Zion was a relatively flat basin near sea level 240 million years ago. As sands, gravels, and muds 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 and those sand dunes are now Zion’s famous sculpted and colorful 2,000 foot cliffs.
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 seabeds 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.
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. This uplift, which is still occurring, 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. 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.
The Virgin River is still excavating. Upstream from the Temple of Sinawava the river cuts through Navajo Sandstone, creating a slot canyon. At the Temple, the river has reached the softer Kayenta Formation below. Water erodes the shale, undermining the overlaying sandstone and causing it to collapse, widening the canyon.
A landslide once dammed the Virgin River forming a lake. Sediments settled out of the quiet waters, covering the lake bottom. When the river breached the dam and the lake drained, it left behind a flat-bottomed valley. This change in the character of the canyon can be seen from the scenic drive south of the Zion Lodge near the Sentinel Slide. (This slide was active again in 1995, damaging the road.)
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.
The North Fork of the Virgin River begins north of Zion at Cascade Falls, where it drains out of Navajo Lake at 9,000 feet above sea level. The East Fork of the Virgin River originates above Long Valley. Both the North and East Forks of the Virgin River run through the park and empty into Lake Mead at about 1000 feet above sea level, where it joins the Colorado River. Though the Virgin River is relatively small, it is incredibly steep. The river drops roughly 7,800 feet in the 160 miles it travels. In the park, the river drops an average of 71 feet every mile. In comparison, the Mississippi River drops about one inch every mile. This steepness, caused by the uplift of the Colorado Plateau, has given the Virgin River the ability to cut through sandstone and carve canyons. Though most of the year the Virgin River runs an average of 100 cubic feet per second, it transports about one million tons of sediment every year. Most of this sediment transport occurs during floods, when the river can swell to thousands of cubic feet per second. These flood events can carry large boulders and rip cottonwood trees out of the ground. It is this powerful force of water that continues to carve the canyon.