Zion National Park Geology - Zion is part of a vast picture; one that includes other Parks and Monuments in the Southwest. Looking at a topological map reveals Zion is located on the western edge of the Colorado Plateau. Also scattered about the plateau are Bryce Canyon National Park, Grand Canyon National Park and Cedar Breaks National Monument which together build the five steps and risers of the geologic area known as the Grand Staircase. Over 200-million years ago, the area where Zion is today was a great desert basin. Over vast spans of time, mountains eroded and material was transported by slow-moving streams and rivers depositing sand in a vast basin. Conditions and the environment changed as time passed and sea water covered dunes of sand. Calcium carbonate cemented loose grains of sand making hard sandstone. The seabed turned to limestone and mud and clay changed to mudstone and shale, forming the sweeping diagonal cross-bedding that Zion National Park is famous for.
Geology of Zion Canyon - Geology of Zion Canyon - The basin lowered due to the weight of the deposits and more time passed as the earth shifted and forced the plateau up, slowly and irregularly and the sea drained away. Streams flowed over the edge of the plateau empowering debris to move at a great rate. This process carved Zion Canyon forcing vertical retreat of canyon walls. Oddly, this occurred in an area where the Navajo sandstone was, at its thickest, only 2000 feet. Today, the North Fork of the Virgin River continues to move debris and erode the canyon, moving an average of 5000 tons of rock fragments daily. Although consistent efforts by the river do some of the work, it is flash flooding that holds the power and force to makedrastic changes. In fact, ninety-percent of the carving is from flash floods. A large flood can result in an astonishing 9000 cubic feet of water per-second to rage down the river. The result is Zion Canyon is becoming deeper at a rate of 600 per-million years.
Zion Will Become Sand Dunes Once Again
The rock formations that exist today in Zion are still changing. Slowly, over vast amounts of time, great monoliths will return to the sand dunes from where they were born in ancient days. Forces of nature make their way through layers of sedimentary rock every day of our future, just as they have in our past. The largest monolith in the world, the Great White Throne, will slowly crumble to sand. Entering Zion from the east side, one of the first sites you will notice is Checkerboard Mesa.
East side of Zion - The east section of Zion National Park is known as slickrock country where rocks are a mixture of white and varied tints of brown or orange. This is a result of minimal iron-oxide compared to other layers of sandstone. Zion slickrock showcases the powerful effects of erosion over a great period of time.
Zion-Mt. Carmel Tunnel - The geology of Zion transforms dramatically when moving from the east section of the park through Zion's longer tunnel. The 1.1 mile-long tunnel was blasted and forged through thick Navajo sandstone during the early 1900's. Imagine cutting through 2000 foot thick sandstone with the machinery available at that time. The Zion-Mt. Carmel Tunnel was a network of scaffolding, set up on the east side of the tunnel going across Pine Creek which flows below. Blasting was used to enlarge the hole and railcars hauled off debris. On the tunnel's south side, work was not an easy task because the drop-off of the canyon below is 800 feet. It is amazing that in the 1930’s; this sort of engineering was accomplished. The whole process is considered a technological wonder and creating the Switchbacks, leading up to the tunnel, was even more difficult.
Eastside Hoodoos - The hoodoos on the east side of Zion are whimsical rock formations twisted and manipulated into various shapes and sizes. Hoodoos in the park vary far more than the uniform hoodoos of nearby Cedar Breaks National Monument and Bryce Canyon National Park.
Checkerboard Mesa Geology - Deep furrows in the shape of a checkerboard game, took millions of years to cut into the sandstone of Checkerboard. The horizontal furrows were made during the Jurassic period by wind-blown sands of huge ancient dunes spread out over land in place of the massive monoliths you see in Zion today. A freeze and thaw process is responsible for gradually widening the furrows along vertical joints. Notice that the carvings are always on the north side where snow takes longer to melt. The vertical slits were created much later after brittle rock had formed. There are etched patterns on smaller surfaces in the park, such as along the East Rim and Hidden Gardens. Past the east side of the park along US-89 between Kanab and Mt. Carmel Jct. evidence of crossbedding can also be found.
Zion National Park, Utah
History of the Thunderbird
Stay in the heart of the parks, Mount Carmel Junction, and visit the treasures of the Southwest and Utah.
This is my new favorite quote:
"I don't know who Tanya Milligan is, but I mean www.zionnational-park.com
It's a better site than the NPS's anyway."
Written by the authors of the book: Favorite Hikes in and around Zion National Park