Take a look anywhere along Zion Canyon and you’ll see 1,600-2,200-foot cliffs of Navajo sandstone. The big walls of Zion were formed from sand dunes deposited during a hot dry period about 200 million years ago. Shifting winds blew the sand from one direction, then another—a careful inspection of the sandstone layer reveals the diagonal lines resulting from this “cross-bedding.” The soaring Navajo sandstone cliffs that form such distinctive features as the Great White Throne and the Three Patriarchs were originally immense sand dunes.Studies by researchers at the University of Nebraska-Lincoln conclude that the vast dunes of southern Utah were formed when the landmass on which they sit was about 15 degrees north of the equator, at about the same location as Honduras is today. The shift patterns apparent in the sandstone—the slanting striations easily seen in cliff faces— were caused in part by intense monsoon rains, which served to compact and move the dunes each rainy season.
Eventually, a shallow sea washed over the dunes. Lapping waves left shells behind, and as the shells dissolved, their lime seeped down into the sand and cemented it into sandstone. After the Colorado Plateau lifted, rivers cut deeply through the sandstone layer. The formation’s lower layers are stained red from iron oxides.
Faulting has broken the Colorado Plateau into a series of smaller plateaus. At Zion you are on the Kolob Terrace of the Markagunt Plateau, whose rock layers are younger than those of the Kaibab Plateau at Grand Canyon National Park and older than those exposed on the Paunsaugunt Plateau at Bryce Canyon National Park.
The rock layers at Zion began as sediments of oceans, rivers, lakes, or sand dunes deposited 65-240 million years ago. The soaring Navajo sandstone cliffs that form such distinctive features as the Great White Throne and the Three Patriarchs were originally immense sand dunes. Look for the slanting lines in these rock walls, which result from shifting winds as the sand dunes formed. Calcium carbonate in the sand piles acted as a glue to turn the dunes into rock, and it’s also responsible for the white color of many of the rocks. The reddish rocks are also Navajo sandstone, but they’ve been stained by iron oxides—essentially rust.
Kayenta shale is the other main rock you’ll see in Zion. For an up-close look, check out the streambed at Middle Emerald Pool. The rippled gray rock is Kayenta shale. This shale, found beneath the Navajo sandstone, is much less permeable than the sandstone. Water can easily trickle through the relatively porous sandstone, but when it hits the impermeable Kayenta shale, it runs along the top surface of the rock and seeps out on the side of the nearest rock face. Weeping Rock, with its lush cliffside springs, is a good place to see the boundary between Navajo sandstone and Kayenta shale.
Although some erosive forces, like flash floods, are dramatic, the subtle freezing and thawing of water and the slow action of tree roots are responsible for most of the changes in the landscape.A gradual uplift of the Colorado Plateau, which continues today, has caused the formerly lazy rivers on its surface to pick up speed and knife through the rock layers. You can really appreciate these erosive powers during flash floods, when the North Fork of the Virgin River and other streams roar through their canyons. Erosion of some of the Virgin River’s tributaries couldn’t keep up with the main channel, and they were left as “hanging valleys” on the canyon walls. A good example is Hidden Canyon, which is reached by a steep trail up from Zion Canyon.
Although some erosive forces, like flash floods, are dramatic, the subtle freezing and thawing of water and the slow action of tree roots are responsible for most of the changes in the landscape. Water seeps into the Navajo sandstone, accumulating especially in the long vertical cracks in the cliffs. The dramatic temperature changes, especially in spring and fall, cause regular freezing and thawing, slowly enlarging the cracks and setting the stage for more dramatic rock falls. Erosion and rock falls continue to shape Zion Canyon. In 1995 a huge rock slide blocked the Zion Canyon Scenic Drive and left hundreds of people trapped at the lodge for several days until crews were able to clear a path.
Flora and Fauna
Many different plant and animal communities live in the rugged terrain of deep canyons and high plateaus. Because the park is near the meeting place of the Colorado Plateau, the Great Basin, and the Mojave Desert, species representative of all three regions can be found here.
Only desert plants can endure the long dry spells and high temperatures found at Zion’s lower elevations; they include cacti (prickly pear, cholla, and hedgehog), blackbrush, creosote bush, honey mesquite, and purple sage. Cacti and yucca are common throughout the park. Pygmy forests of piñon pine, Utah juniper, live oak, mountain mahogany, and the fragrant cliffrose grow at elevations of about 3,900-5,600 feet.
In early spring, look for the Zion shooting star, a plant in the primrose family found only in Zion.Once you get above the canyon floor, Zion’s plants are not so different from what you’d find across the West. Trees such as ponderosa pine and Douglas fir can thrive here thanks to the moisture they draw from the Navajo sandstone. White fir and aspen are also common on high cool plateaus. Permanent springs and streams support a profusion of greenery such as cottonwood, box elder, willow, red birch, horsetail, and ferns. Watch out for poison ivy in moist shady areas.
Colorful wildflowers pop out of the ground—indeed, even out of the rocks—at all elevations, spring-fall. In early spring, look for the Zion shooting star, a plant in the primrose family found only in Zion. Its nodding pink flowers are easily spotted along the Emerald Pools trails and at Weeping Rock. You’re also likely to see desert phlox, a low plant covered with pink flowers, and, by mid-May, golden columbine.
Mule deer are common throughout the park. Also common are bank beavers, which live along the banks of the Virgin River rather than in log lodges, which would be too frequently swept away by flash floods. Even though they don’t build log lodges, they still gnaw like crazy on trees—look around the base of riverside trees near Zion Lodge for their work. Other wildlife includes elk, mountain lions, bobcats, black bears, reintroduced bighorn sheep, coyotes, gray foxes, porcupines, ringtail cats, black-tailed jackrabbits, rock squirrels, cliff chipmunks, and many species of mice and bats.
Birders have spotted more than 270 species in and near the park, but most common are red-tailed hawks, turkey vultures, quail, mallard, great horned owls, hairy woodpeckers, ravens, scrub jays, black-headed grosbeaks, blue-gray gnatcatchers, canyon wrens, Virginia’s warblers, white-throated swifts, and broad-tailed hummingbirds. Zion’s high cliffs are good places to look for peregrine falcons and the park’s reintroduced California condors; try spotting them from the cliff at Angels Landing trail.
Hikers and campers will undoubtedly see northern sagebrush lizards, and they should watch for Western rattlesnakes, although these relatively rare reptiles are unlikely to attack unless provoked.