Friday, January 28, 2011

The Grand Staircase section of the Grand Staircase-Escalante National Monument


Good viewing spots of the entire staircase are hard to come by. The curvature of the Earth also obstructs distant areas from view. One of the best is south of Kanab, Utah along Route 89A in Arizona, somewhat north of the Grand Canyon, which is where this photo was taken.
 
 

 

President Clinton created the 1.9-million-acre Grand Staircase-Escalante National Monumenton September 18, 1996. Placed under the management of the U.S. Bureau of Land Management, it is located in south-central Utah. The monument is located within the Colorado Plateau physiographic province, near its western margin. It contains an astounding array of paleontological, geological, archaeological, biological and historical resources. Largely located in a remote area, it is comprised of mesas and cliffs, and canyons and plateaus, and distinguished by colorful geologic formations.  

 
The three sections of the Grand Staircase-Escalante National Monument:
the Grand Staircase section in blue; the Kaiparowits Basin section in yellow;
and the Escalante Canyons section in green.
From Geology of Grand Staircase-Escalante National Monument, Utah by Doelling et al
 

Cross-sectional Diagram of the Grand Staircase
from Geology of Grand Staircase-Escalante National Monument by Doelling et al 

RISERS AND CLIFFS, STEPS AND BENCHES 
The monument is divided into three geographical sections from west to east; the Grand Staircase, the Kaiparowits Basin and Escalante Canyons. More than 275 million years of Earth’s history are exposed in its rock formations extending from the Permian to the Cretaceous. The Grand Staircase section encompasses the western third of the monument. It refers to an immense sequence of sedimentary rock layers that form a series of topographic benches and cliffs that steps up in elevation progressively from south to north.

The staircase's risers correspond to cliffs, each rising as much as 2,000 feet, and the steps correspond to the benches, terraces, or plateaus in the staircase. The staircase generally includes the region from the Kaibab Uplift and Plateau, which forms the north rim of the Grand Canyon at the bottom of the staircase, to the Pink Cliffs of Bryce Canyon, at the top. 

GENESIS OF THE STAIRCASE 
The Grand Staircase began to form when vast Cambrian oceans lapped onto the broad continental shelves of the still-forming North American continent. Later, Triassic rivers and streams in their flood stages left silty and muddy deposits on the ancient landscape. Then, sandy “seas” the size of the Sahara deposited windblown sand dunes during the Jurassic. Next an enormous, shallow inland, Cretaceous sea left mud, silt and sand on its fluctuating shoreline and sea floor. Lastly, a Paleogene system of lakes deposited layer after layer of their limey deposits.

All these ancient geological events occurred in succession, one after the other, depositing a legacy of their presence that was written in stone. Laramide uplift elevated and tilted the staircase's Paleozoic and largely Mesozoic rocks to their existing location, along with the Colorado Plateau as a whole and the Grand Canyon to the south. As erosion attacked the staircase, scarps formed where several soft layers were capped by harder ones. The scarps are aligned approximately  northwest, parallel to the strike of the strata, given the northeast dip of the staircase. Subsequently, erosion retreats the strata to the northeast, down the dip of the strata. 

The Stratigrpahic Units of the Grand Staircase
from Bryce Canyon National Park and the Grand Staircase by Foos
 
COLORED CLIFFS
The cliffs are named by their colors. Starting from the bottom, they are the low cuestas of the Chocolate Cliffs capped by the resistant, Triassic sandstone of the Shinarump Conglomerate, the grand Vermilion and White Cliffs held up by the Wingate and Navajo Sandstones respectively, the Gray Cliffs of Cretaceous shales and sandstones, and at the top, the Paleogene Claron Formation comprising the Pink Cliffs. 

 
The Stratigraphic Units of the Grand Staircase
from Bryce Canyon National Park and the Grand Staircase by Foos


This diagram shows the Grand Staircase from the bottom of the Grand Canyon to the very top at Bryce Canyon.
The vertical perspective is greatly exaggerated. The lower diagram, drawn to more realistic proportions,
is more realistic of the actual topography. Click the diagram for a larger version. Diagrams from Ancient Landscapes of the Colorado Plateau by Ron Blakey (Colorado Plateau Geosystems, Inc.) and Wayne Ranney.
P.S. This book is a must read!

Probably named by the early geologist Clarence Dutton in the 1880’s, the Grand Staircase’s alternating configuration of southward-facing cliffs, terraces, and slopes is due to the varied erosion rates of the different rock types. Harder rocks, such as sandstone and limestone, erode slowly and make up the cliffs and terraces. Softer rocks, such as shale and siltstone, erode faster and make up the slopes. This high, rugged, and remote region, where bold plateaus and multi-hued cliffs run for distances that defy human perspective, was the last place in the continental U.S. to be mapped.

3 comments:

  1. Jack - A most excellent post with great graphics to show the concepts. You are showing my blog up!! Nice work. Keep it up.

    ReplyDelete
  2. Awesome views, I really love it. Please keep on posting!

    Click Here

    ReplyDelete
  3. I drove the Cottonwood road out of Cannonville off 12 to Grosvenor Arch, bright yellow 90 ft. above me in 2012. The Coxcomb took me further south through Pariah Box to US 89 and the Vermillion Cliffs and Kanab-to Coral Pink Sand Dunes and Zion. What country!

    ReplyDelete