Grand staircase

The Cockscomb ( Hahnenkamm ) runs along Cottonwood Canyon Road

The Grand Staircase ( Grand Staircase ) is a cuesta landscape , resulting in the sedimentary rocks of the Colorado Plateau in the western United States has emerged. It extends in the states of Utah and Arizona from Bryce Canyon National Park to the south via Zion National Park to the Grand Canyon .

Location and name

The area known as the Grand Staircase is roughly equally divided between Utah in the north and Arizona in the south. The southern limit is formed by the Grand Canyon, the northern limit by the Paunsaugunt Plateau in southern Utah. The eastern border is formed by the jagged ridge of the Cockscomb ( Hahnenkamm ), which lies in the area of the East Kaibab Monocline , a large curvature of the strata at which the rock strata lying further west in the subsurface spread out into the air. The western limit is the Hurricane Cliffs above the Kolob Canyon system .

Geological profile of the Grand Staircase. Red dots from left to right: Pink Cliffs, Gray Cliffs, White Cliffs, Vermilion Cliffs, Chocolate Cliffs

The originator of the name is unclear, it possibly goes back to the geologist Clarence Dutton , who in 1870 imagined the ascent to the north from the Grand Canyon, structured by a series of steep walls and flat terrain, as a staircase. Dutton divided the layer cake-like sequence from top to bottom into five sections:

Pink Cliffs
Gray Cliffs
White Cliffs
Vermilion Cliffs
Chocolate Cliffs

Since then the levels have been subdivided geologically even more finely.

geology

The geology of the Grand Canyon and its surroundings is determined by five main units, the age of which is between 2000 million and 600 million years, and which are divided into almost forty sub-units. There are numerous links between the rock units in the Grand Canyon, Bryce Canyon, and Zion Canyon.

The oldest exposed formation in Zion National Park is the youngest in the Grand Canyon - the 240 million year old Kaibab Limestone . The area around Bryce Canyon in the northeast begins where the rocks of the Zion area end, and is made up of Cenozoic rocks that are about 100 million years younger. In fact, the Zion Territory's youngest formation, the Dakota Sandstone , is the oldest in Bryce Canyon. Nevertheless, the three areas share a common sequence of layers, the Grand Staircase.

This sequence of layers began to emerge at the beginning of the Tertiary about 65 million years ago. It was raised a total of 1500 to 3000 m, partly inclined and bent. These movements go back to the Laramian orogeny . As a result, the Colorado and its tributaries cut into the rock. However, the great plateaus did not form until about five to six million years ago when the Gulf of California opened up and deepened the drainage base of the Colorado.

The sequence of steep steps and flat pieces goes back to the alternating layers of rocks of different resistance. Hard rocks such as sandstone and limestone are only slowly removed, while soft marls and mudstones offer little resistance. For this reason, the plateaus are formed by clearing away the softer surface layers over the surfaces of the hard rock. The steep walls result from a combination of factors: The soft rocks lying under the hard rock are continually eroded in geologically short periods of time, so that the overlying layers repeatedly tumble down and form fresh fragments. At the same time, the stability of the rock ensures the formation of steep walls.

paleontology

In the 1880s, many large dinosaur skeletons were unearthed north of the Grand Staircase in southern Utah . After these discoveries, little more research was done. Towards the end of the 20th and the beginning of the 21st century, however, interest in the exploration of the largely unexplored fossil content of the layers of the Grand Staircase reawakened.

Fossilized skeleton of a young Hadrosaurus
exhibit at the Grand Staircase-Escalante National Monument

Southern Utah has therefore not ceased to be a worthwhile destination for researchers due to the interaction of its climatic conditions and its rocks, as fossils can repeatedly be exposed and collected on the surface. In the south, in Arizona, the climate is so dry that erosion is slow. In the north, the climate allows trees and forests to grow, not only reducing erosion, but also root growth and the activity of soil-dwelling bacteria leading to the destruction of fossils.

In southern Utah, on the other hand, the climate is too dry for a vegetation cover to form, and the episodic occurrence of storms and cloudbursts leads to rapid erosion, which repeatedly exposes new fossils.