Zion National Park - Utah
Zion National Park is part of the Southwest's "Grand Circle" of national parks, monuments, historical and recreational areas. This Grand Circle is located on the Colorado Plateau, so-named because it is a large uplifted area of land in the Four Corners area of the Southwest through which the Colorado River flows. The Colorado Plateau contains one of the world's greatest concentrations of natural and cultural features, due primarily to its geology, revealed by the Colorado and other rivers.
Mormons started settling and farming the Virgin River region in 1847. Their search for farmland led them to Zion Canyon in 1858, about 75 miles up the Virgin River from the confluence of the Colorado and Virgin Rivers, below the Grand Canyon.
After his difficult passage through the Grand Canyon in 1869, Major John Wesley Powell was inspired to complete the task of surveying the whole Colorado River region. His exploration party included geologists Clarence Dutton and Grove Karl Gilbert, photographer Jack Hillers, and artist William H. Holmes, all famous names in the history of scientific exploration in the American West. Over the next two decades, these scientists pieced together a picture of time and the land on a giant scale. They discovered how, through periods of geologic history, the Colorado Plateau was uplifted while river systems steadily cut down through numerous layers of sedimentary rocks.
Powell and Gilbert made a geological reconnaissance of Zion Canyon in 1872 and named several features. Later, Dutton conducted extensive mapping of the area. It was their glorious reports, along with Hillers' photographs and Holmes' drawings, that first created fascination with Zion nationally. In 1903, artist Frederick S. Dellenbaugh painted scenes in the canyon and exhibited his work at the St. Louis World's Fair. This public attention led to President Theodore Roosevelt proclaiming the area a national monument in 1909 (called Mukuntuweap at the time). The U.S. Congress established Zion National Park in 1919; additional areas were included in the park in 1937 and 1956.
The Zion-Mt. Carmel highway (Utah 9), an engineering marvel of its time, was opened in 1930 to provide access to Zion. From the park's east entrance, the highway leads to the famous Pine Creek Tunnel, which is more than a mile long and has six large windows cut into the rock for views. From the tunnel, switchbacks go down to the scenic drive on the floor of Zion Canyon.
- Mukuntuweap National Monument proclaimed July 31, 1909.
- Incorporated in Zion National Monument by proclamation March 18, 1918.
- Established as national park Nov. 19, 1919.
- Separate Zion National Monument proclaimed Jan. 22, 1937; incorporated in park July 11, 1956.
- Other boundary changes: June 13,1930; June 3, 1941; Feb. 20,1960; Oct. 21,1976.
The geologic history of Zion Canyon begins where the history of the Grand Canyon, 120 miles to the southeast, ends. The rock sequence in Grand Canyon National Park is primarily Precambrian and Paleozoic and covers about two billion years. Zion formations are Mesozoic and represent only about 150 million years of geologic time. The top layer of the Grand Canyon, Kaibab limestone, is the bottom layer of Zion National Park.
The great variety of landform shapes in Zion that fascinated early explorers are the result of a combination of factors. Resistant (sandstone) and nonresistant (shale) types of bedrock have been weathered with strange effects. Access to the interior of the layered rocks is provided by many bedding planes, joints and faults of curved, horizontal or vertical orientation.
Frost action has significant effects, mainly at higher elevations on the canyon rims and on the plateau where there are more freeze-thaw days and more moisture is available. Rainwater, seepage, and tree roots are also effective agents of weathering, even in the arid to semiarid climate of southern Utah.
Navajo Sandstone is porous enough so that water percolates through it. On its downward path, some water seeps out along fractures and bedding planes and drips off the cliff face; still more water collects along the top of an impermeable rock layer and flows out in a spring. On Weeping Rock in Zion Canyon, hanging gardens of wildflowers adhere to dripping crevices in the wall above a spring. Weeping Rock is the loveliest of the numerous springs issuing from the "spring line" between the Navajo and Kayenta Formations. (The Kayenta is an impermeable shale.)
The "temples" are the result of resistant, unfractured rock standing as columns or pyramids after the highly fractured rock between has been eroded and transported away. Examples are East Temple, Checkerboard Mesa, Sentinel Mountain, Twin Brothers, Temple of Sinawava, West Temple, the Three Patriarchs, Towers of the Virgin, and the Beehives.
Navajo Sandstone Formation
Navajo Sandstone is the rock dominating Zion National Park. This massive formation is 1500 to 2000 feet thick and is characterized by its cross-bedding, because it developed from ancient sand dunes. Some lower parts of the formation were deposited in shallow water with the cross-bedding caused by currents. The Aeolian (windblown) cross-bedding formed as shore dunes were affected by prevailing winds. Any
shift in wind direction intensifies the cross-bedding effect. The most striking cross-bed sets are displayed in the upper parts of the Navajo Formation, like those found in Checkerboard Mesa and other cliffs along the Zion-Mt. Carmel highway.
The Great White Throne is a natural feature sculpted by erosion of the Navajo Sandstone. It is actually a large monolith rising about 2450 feet from the canyon floor. The color of the throne, the upper part of the monolith, is really a light tan; but from a distance with sunlight is striking it, it appears to be a brilliant white. The base of the throne is stained deep red due to iron oxide leaching out from higher rock layer. The Great White Throne is an example of how the lower beds of the Navajo Sandstone formation are likely to form vertical cliffs, while the upper portions are likely to weather as rounded domes.
Chinle Shale Formation
The colorful purple-gray Chinle Formation is exposed near Cougar Mountain and the Taylor Creek trailhead in the Kolob section. The sediments composing the Chinle are a mixture of sandstone, shale, limestone and volcanic ash. The volcanic ash is fascinating because it provided the silica necessary for wood petrification in the Chinle Formation. Pieces of petrified wood weather out of Chinle beds in the Zion region and other parts of the Colorado Plateaus, most notably, at Petrified Forest National Monument.
The only igneous rocks in the park are young basaltic lavas that broke through to the surface along north-south normal faults lines. One flow, about one half million years ago, flooded and dammed the Coalpits Wash drainageway in the southwest corner of the park. After the lava cooled, a large lake filled the wash. Crater Hill, a cinder cone, represents the last eruption in the Coalpits Wash. Eventually, as the lake filled with sediment, a spillway developed that gullied and drained off the water. The Coalpits Wash is now the driest, most desolate area in the park. Lava Point, near the northern edge of the park, and Horse Ranch Mountain in the Kolob section, are also locations accessible by trails.
Zion Canyon, is a deep chasm with nearly vertical walls. It was cut by the North Fork of the Virgin River, whose great erosive power is due to its gradient, or slope, which ranges between 50 and 80 feet per mile. This action was caused by the general uplifit of the Colorado Plateau during the Tertiary Period (60-20 million years ago). The river transports almost 3 million tons of rock and sediment downstream annually.
Because the Virgin River is downcutting more rapidly than its tributaries with smaller volumes of water, they are left with their valley floors at a higher level than the floor of the Virgin River. These "hanging valleys" connect by waterfalls with the river below, but because they also have smaller drainage basins, some of them are intermittent, flowing only during wet seasons. Angels Landing is a typical hanging valley, as are the valleys between Twin Brothers peaks and Mountain of the Sun (located on the eastern side of the canyon north of Pine Creek).
Geologists estimate that the Virgin River can cut down another thousand feet and still have enough energy to carry sediment to the Colorado River. The erosive power of sediment-laden water running at high velocity is demonstrated in the celebrated Narrows at the head of Zion Canyon.
Here the stream runs through an erosion-enlarged fracture about 12 miles long. The floor is only a few feet wide, but the enclosing walls rise about 2000 feet, nearly straight up. Sunlight reaches the streambed only when the sun is directly overhead. When the water level is low, visitors are permitted to hike through the Narrows. However, the canyon walls are so close to each other that the water level may rise 25 feet in 15 minutes during a heavy rain or flash flood.
Mass wasting in Zion Canyon is gradually widening the valley, and in many places the canyon rims are developing a scalloped look as they retreat unevenly. Springs, undermining of sandstone cliffs as the softer underlying shales give way, has caused the sandstone cliffs to become overhanging, and then, due to lack of support, great chunks of rock, sometimes weighing several tons, break loose and fall to the canyon floor.
Sometimes a "blind arch," or inset arch, forms on a cliff face when the upper rock layers remain intact after the lower part has fallen. An important example is Great Arch on a cliff that can be seen from tunnel windows on Route 9. Great Arch is 600 feet across its base and stands 400 feet high. Some arches, such as Kolob Arch in the Kolob section of the park, have become freestanding instead of inset. With a span of 310 feet, Kolob is the largest freestanding arch in the world.
Slump blocks are large masses of material that slide downhill as a coherent unit. They are another example of mass wasting in Zion National Park. Mudstone layers in the Kayenta Formation, underlying the Navajo Sandstone, become slippery when saturated with water. Sometimes, when the mudstone gives way, slump blocks of the Navajo break loose along vertical fractures, sliding down to the canyon floor.
About 4000 years ago, a great slump block in Zion Canyon dammed the Virgin River and created a lake that backed up in the canyon as far as Weeping Rock. Lake-bottom deposits accumulated on the canyon floor until the Virgin River was able to cut through the slump and drain the lake. Eventually all traces of the former lake will be removed and the river will resume downcutting bedrock in that part of the canyon.
Earthquakes in the Colorado Plateau region often trigger landslides and rockfalls. A 5.6 earthquake in 1933 was responsible for a large landslide at the west entrance of Zion National Park. The landslide continued to move for 9 hours after the quake, perhaps because of water beneath the surface under the landslide. The epicenters of these quakes are often a great distance from Zion, yet they can still exert dramatic effects.
Zion National Park
Springdale, UT 84767-1099
Vistor information 435-772-3256
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