The Kaibab Monocline

            During our Geology Field Studies trip to the Grand Staircase - Escalante National Monument the class camped within a structure called the Kaibab Monocline.   To the right is a cross section of the Kaibab Monocline as it looks near the North Rim of the Grand Canyon.   A monocline is a one-sided fold.  This particular one stretches north-south for about 240 km and dips steeply to the east  - up to 60^o-70^o.  This monocline was formed by subsurface movement on a fault during the Laramde Orogeny between 50 and 80 million years ago.  (Tindall, 2000).

Differential erosion of the tilted rock layers exposed along the monocline has created a series of east dipping ridges and valleys. Differential erosion occurs because less resistant rock layers like shale will wear away more quickly than more resistant rock layers like sandstone.   Here, the less resistant Tropic Shale and Carmel Formations weathered to form valleys, while the more resistant layers like the Navajo Sandstone and Dakota Sandstone formed ridges.  Stream erosion of the ridges creates the triangular hogbacks seen here.   Locally, this is called the Cockscomb. It was the down-warping on the east side of the monocline that allowed the young layers of the Wahweap and Kaipairowits to be protected from erosion.  Had it not been for the monocline, these layers and all the dinosaur bones they contain might have eroded away long before humans came around to discover them.

References

 Reches, Ze'ev. 1977  "Development of monoclines: Part I. Structure of the Palisades Creek branch of the East

Kaibab monocline, Grand Canyon, Arizona." Development of monoclines: Part I. Structure of the Palisades Creek branch of the East Kaibab monocline, Grand Canyon, Arizona. The Geological Society of America, 25 Web. 16 Apr. 2014.    <http://memoirs.gsapubs.org/content/151/235.abstract>.
Tindall, Sarah E. 2000 "The Cockscomb Segment of the East Kaibab Monocline: Taking the Structural Plunge." Geology of Utah's Parks and Monuments 28 pages 1-15.