The Geology of Zion National Park

Designated as Utah's first national park in 1909, Zion is a breathtaking display of nearly 275 million years of geologic history. Its colorful sedimentary cliffs, arches and canyons dominate the landscape for over 229 square miles and are a sight to behold for geologists and non-geologists alike.

Colorado Plateau

Zion shares a similar geologic background as the nearby Bryce Canyon (~50 miles to the northeast) and Grand Canyon (~90 miles to the southeast) National Parks. These three natural features are all part of the Colorado Plateau physiographic region, a large, elevated "layered cake" of sedimentary deposits encompassing much of Utah, Colorado, New Mexico and Arizona.

The region is remarkably stable, showing little of the deformation that characterizes the bordering Rocky Mountains to the east and the Basin-and-Range province to the south and west. The large crustal block is still being uplifted, meaning that the area is not immune to earthquakes. Most are minor, but a 5.8 magnitude quake caused landslides and other damage in 1992.  

The Colorado Plateau is sometimes referred to as the "Grand Circle" of National Parks, as the high plateau is also home to Arches, Canyonlands, Captiol Reef, Great Basin, Mesa Verde and Petrified Forest National Parks. 

Bedrock is easily exposed along much of the plateau, thanks to the arid air and lack of vegetation. The undeformed sedimentary rock, dry climate and recent surface erosion make this area one of the richest troves of Late Cretaceous dinosaur fossils in all of North America. The entire region is truly a mecca for geology and paleontology enthusiasts.

The Grand Staircase 

On the southwestern edge of the Colorado Plateau lies the Grand Staircase, a geologic sequence of steep cliffs and descending plateaus that stretches south from Bryce Canyon to the Grand Canyon. At their thickest point, the sedimentary deposits are well over 10,000 feet. 

In this image, you can see that the elevation decreases in steps moving south from Bryce until it reaches the Vermillion and Chocolate Cliffs. At this point, it begins a gradual swell, gaining several thousand feet as it approaches the North Rim of the Grand Canyon.

The lowermost (and oldest) layer of sedimentary rock exposed at Bryce Canyon, the Dakota Sandstone, is the top (and youngest) layer of rock at Zion. Similarly, the lowest layer at Zion, the Kaibab Limestone, is the top layer of the Grand Canyon. Zion is essentially the middle step in the Grand Staircase. 

Zion's Geologic Story

Zion National Park's geologic history can be broken down into four main parts: sedimentation, lithification, uplift and erosion. Its stratigraphic column is essentially a working timeline of the environments that existed there over the past 250 million years.

The depositional environments at Zion follow the same general trend as the rest of the Colorado Plateau: shallow seas, coastal plains and sandy deserts.

Around 275 million years ago, Zion was a flat basin near sea level. Gravel, mud and sand eroded down from nearby mountains and hills and was deposited by streams into this basin in a process known as sedimentation. The immense weight of these deposits forced the basin to sink, keeping the top at or near sea level. Seas flooded the area during the Permian, Triassic and Jurassic periods, leaving carbonate deposits and evaporites in their wake. Coastal plain environments present during the Cretaceous, Jurassic and Triassic left behind mud, clay and alluvial sand. 

Sand dunes appeared during the Jurassic and formed on top of each other, creating inclined layers in a process known as crossbedding. The angles and inclines of these layers show the direction of the wind during the time of deposition. Checkerboard Mesa, located in the Canyonlands Country of Zion, is a prime example of large-scale horizontal cross-bedding. 

These deposits, separated as distinct layers, lithified into rock as mineral-laden water slowly made its way through it and cemented the sediment grains together. Carbonate deposits turned into limestone, while mud and clay turned into mudstone and shale, respectively. The sand dunes lithified into sandstone at the same angles at which they were deposited and are still preserved in those inclines today. 

The area then rose several thousand feet, along with the rest of the Colorado Plateau, during the Neogene period. This uplift was caused by epeirogenic forces, which differ from orogenic forces in that they are gradual and occur over broad regions of land. Folding and deformation are not normally associated with an epeirogeny. The thick crustal block that Zion was sitting on, with over 10,000 feet of accumulated sedimentary rock, remained stable during this uplift, tilting only slightly to the north. 

Zion's present day landscape was created by the erosional forces that resulted from this upheaval. The Virgin River, a tributary of the Colorado River, established its course as it traveled quickly down newly steepened gradients towards the ocean. Faster moving streams carried larger sediment and rock loads, which quickly cut away at the rock layers, forming deep and narrow canyons. 

Rock Formations at Zion

From top to bottom, or youngest to oldest, the visible rock formations at Zion are as follows: