Geology

Zion National Park can give you a crick in the neck from gaping up at the thick layers for red stone piled on top of each other. The curious — OK, I admit, the nerdy — among us want to know more about all of this stone, and then spout our newly-acquired knowledge to anyone within earshot. What’s it called, we wonder. How did it get there?

You’ve probably heard something about the Grand Staircase, and maybe how Zion fits in to that story somehow.

Geologists love to talk about the stratigraphy of a location, that is, the sequence of layers, and said layers in Zion are in the diagram on the right.

In Zion Canyon, the thick, red, smooth-walled stone is Navajo Sandstone, deposited during the Jurassic period as red sand dunes piled onto more sand dunes, in an area larger than today’s Sahara. The grains are mostly quartz, and the red coloring is from a pervasive spread of iron. This layer is almost 2 thousand feet (600 m) thick. You can get up close to all of this by hiking up through Refrigerator Canyon on the West Rim Trail, or Echo Canyon on the East Rim trail.

Water seeps into the stone, and the Navajo Layer behaves as a large sponge, holding water, but when saturated, letting the excess seep out the bottom. The black stains on the cliff walls are Desert Varnish, which gets its black color from manganese. The latest consensus is that there are living organisms in the varnish.

If you look carefully in this layer, sometimes you can find flaws in the stone, like a thin layer of embedded limestone. Sand dunes have oases, and a long-standing body of water leaves limestone deposits from accretions of carbon.

Down in the bottom of the canyon there’s as much soil as stone, and the walls slope instead of dropping down as sheer cliffs. This is the Kayenta formation, itself a collection of discrete layers. This group is made from river deposits when the area was lower and wetter, a vast riverine plain. These flows left layers of mudstone, shale and in the river beds, sandstone. As you look, you can see lens-shaped cross sections of river beds.

Kayenta layers block the flow of water, providing a barrier and preventing the flows from going deeper. This means that at the bottom of the canyon water flows out from the higher Navajo Layer. If you hike in the Zion Narrows, you can see many springs there, including the largest of them all, Big Spring, a few miles (about 5 k) up-canyon from the Temple of Sinawava.

On the park’s east entrance, the highest part of the park, you can see the Carmel layers, deposited when the area dropped and was submerged with sea water. Calcium carbonate from that water seeped down over time, cementing all of those red sand dunes in the Navajo Layer, turning them into sandstone.

On top of some Carmel formations are caps of limestone, the Dakota formation.

How long ago did all of this stuff happen? If your inner nerd is still not satisfied, memorize some of these periods. This shows you that the late Permian, the lowest level in Zion, goes back 251 million years, and that the newest layers at the top of the park, are from the early Cretaceous, putting them back 145 million years.

What happened to all the layers above that? Blown away in the wind. If you’d like to see some of these higher layers, you can find them at Bryce National Park.

How about older layers? Head to Grand Canyon National Park. The Kaibab Limestone at the top of the park is Permian, taking off about where Zion stops. If you hike to the bottom, you can see Vishnu Schist and Zoroaster Granite, about 2 billion years old.

Find out more about the geology in our National Parks here, brought to us by the United States Geologic Survey. Spend a little time with these diagrams and images and you can start tossing out words like “stratigraphy” as if you knew what you were talking about. You might even satisfy a little of the nerdy curiosity.