Walnut Canyon National Monument
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Stop 20 Walnut Canyon
Location: 10 miles east of downtown Flagstaff, AZ.
Date: March 10, 2007

Walnut canyon was inhabited by Sinagua Indians sometime around 1125 A.D. The region was very undesirable for agriculture because precipitation events either occurred in the winter as large snowfalls or in the summer as intense thunderstorms.  To adapt to the dry climate the Sinagua people build damns in the canyons to trap water to catch water as runoff from the landscape.


View from the top of Walnut Canyon


There are three distinct formations visible at Walnut Canyon (Figure 1 and 2). The upper most layer is composed of cinders from the eruption of Sunset Crater in 1065 AD. Just below the cinders is the Kaibab Formation which is about 277-275 million years old. There are some small fossils present in the Kaibab formation indicating the rock was formed in a shallow ocean environment.  These fossils include brachiopods, crinoids, and sponges.


Geologic history of Walnut Canyon


The cliff dwellings are located in the Kaibab formation due to its soft erodeable nature.  Between the Kaibab formation and the lower Coconino formation is a unconformity. Below this unconformity lies the Coconino sandstone formation which is about 272-271 million years old. 


Cliff dwellings in the Kaibab formation


The Coconino sandstone was one a desert environment along a sea coast where white and tan sands were shaped into dunes.  There is visible cross bedding in the dunes which indicates a cemented sand dune.


Visible cross bedding of Coconino Sandstone.


Walnut Canyon was still near sea level in the late cretaceous, about 80 million years ago.  Tectonics uplifted the Colorado Plateau, causing large amounts of erosion from rivers.  The upper layers of the plateau were very soft and the rivers such as Walnut Creek meandered back and forth over time.  When Walnut Creek down-cut into the more resistive Kaibab Layer the river formed an entrenched meander (what is now known as Walnut Canyon).  This happened about 6 million years ago.  More recently Walnut Creek deposited alluvium at the bottom of the canyon, slowly filling in the canyon.


The formation of Walnut Canyon.



By W. Patrick Dryer