Thursday, July 02, 2020

Geology of the National Parks Through Pictures - Canyon de Chelly NM

My next post about the Geology of the National Parks Through Pictures was from a rather snowy trip to Arizona where my wife ran an Ironman and then we did a tour of some of Arizona's National Parks, that unfortunately got snowed out towards the end of the trip.

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website

Arizona State Geological symbols can also be found HERE.


Canyon de Chelly National Monument
Our final park this trip, after a shortened visit to Petrified Forest and needing to skip another park entirely was Canyon de Chelly, which we ended up staying the night at the park hotel. Because of the snowstorm, the roads ended up being a bit hit or miss, with the lower elevation roads practically snowless and the higher elevation roads nearly impassable.

The entrance sign. The name of the canyon is a Spanish corruption of the Navajo word "Tsegi" meaning rock canyon. The pronunciation of "de Chelly" has slowly morphed over time from the Spanish "day shay-yee" to the modern day pronunciation of "d'SHAY". 

Canyon de Chelly is a unique park, since it is an actively lived in park. The park is run in conjunction with the Navajo Nation, where members of the Navajo Nation also live in the park and actively help preserve the ancient cliff dwellings within the walls of the canyon. The park is composed of several canyons, the primary two being Canyon de Chelly (the southern canyon with views from the road facing north) and the northern canyon, Canyon del Muerto, with views towards the south. The two canyons split off from each other towards the visitor's center.

When we arrived in the evening, we were advised to do the southern rim drive, along Canyon de Chelly, first. Then hold off and do the northern rim drive, along Canyon del Muerto, in the morning to get the best light in both. This is a view from Tunnel Overlook up the end of the Canyon de Chelly before the Canyon del Muerto splits off.

 A little bit further along the canyon, this is a view across the Canyon de Chelly from the Tsegi Overlook.

 View from the next stop at Junction Overlook. The canyon is made up almost entirely of one rock unit, the De Chelly Sandstone, which is a Permian age (~200 million years old) aeolian sandstone. Aeolian means that it is formed by blowing wind, in particular sand dunes, or a desert environment. When sand dunes are frozen in time, such as when they become rocks, and eroded you can see features termed cross-bedding. These rock preserve an ancient desert that used to be located here. We will look a little bit more into cross-bedding in a later photograph below.

Canyonlands National Park stratigraphy
A cross section of the Canyon de Chelly National Monument geology from the USGS. Although most of the canyon walls are composed of sandstone, there is a bit of the Triassic age Shinarump Conglomerate along the tops of the cliffs and the older Permian Organ Rock Formation along the base of the canyon.

View from the White House Overlook, looking down on the White House cliff dwelling. Many of the cliff dwellings on the southern side are not as easily seen from the road, however we can get a closer look at some of the later houses.

Here is the Face Rock overlook with the cliff dwellings located within the center of the cliff face in the center of the photograph.

A zoomed in view of the Face Rock cliff dwellings. These, and most of the cliff dwellings in the park, were built between 1100 and 1300 CE by the ancestral Puebloan people before the arrival of the modern day Navajo. This time period corresponds with other cliff dwellings in the region such as Mesa Verda and Tonto National Monument.

Along the Canyon del Muerto on the northern part of the park there are not as many overlooks but the views of the cliff dwellings are far better. This is the first stop along the northern rim at Antelope House Overlook with Antelope House below the cliff on the right part of the image.

Here is a closer up view of Antelope house. The buildings were constructed using a combination of the De Chelly Sandstone as building blocks and adobe bricks that were created from the mud and baked.

View from the Mummy Cave overlook. The cliff dwellings are located along the left side of the photo.

Close up view of the Mummy Cave cliff dwelling.

Yucca Cave cliff dwellings.

View up Canyon del Muerto at Massacre Cave Overlook.

View at the Massacre Cave Overlook with the cross-bedding in the De Chelly Sandstone highlighted by the snow. The cross-bedding is the angular lines through the sandstone layers. While here the layers of sandstone are generally horizontal, the cross-bedding is at an angle. The way cross bedding forms within a dune is illustrated below:

Cross Bedding
As sand is pushes up over a dune by the wind, the sand grains form parallel lines on the slipface of the dune. These parallel lines of the grains are what we see preserved within the rock. Image from


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