Grand Staircase
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The Grand Staircase is an immense sequence of sedimentary rock layers that stretch south from Bryce Canyon National Park through Zion National Park and into the Grand Canyon. In the 1870s, geologist Clarence Dutton first conceptualized this region as a huge stairway ascending out of the bottom of the Grand Canyon northward with the cliff edge of each layer forming giant steps. Dutton divided this layer cake of Earth history into five steps:
Since then, modern geologists have further divided Dutton's steps into individual rock formations.
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What makes the Grand Staircase worldly unique is that it preserves more Earth history than any other place on the planet. Geologists often liken the study of sedimentary rock layers to reading a history book--layer by layer, detailed chapter by detailed chapter. The problem is that in most places in the world, the book has been severely damaged by the rise and fall of mountains, the scouring of glaciers, etc. Usually these chapters are completely disarticulated from each other and often whole pages are just missing. Yet the Grand Staircase and the lower cliffs that comprise the Grand Canyon remain largely intact speaking to over 600 million years of continuous Earth history with only a few paragraphs missing here and there.
Unfortunately, the Grand Staircase is such a vast region of rock that no matter where you stand on its expanse, most of it will be hidden behind the curvature of Earth. Places such as Yovimpa Point and the north slope of the Kaibab Plateau are the exception where even a non-geologist can discern the individual chapters of this colossal history book--these immense steps of Dutton's Grand Staircase.
Geology
The major sedimentary rock units exposed in the Grand Canyon range in age from 2000 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world. See geology of the Grand Canyon area for details.
The oldest exposed formation in Zion National Park is the youngest exposed formation in the Grand Canyon - the ~240 million year old Kaibab Limestone. The Bryce Canyon area to the northeast continues where the Zion area leaves off by presenting Cenozoic-aged rocks that are 100 million years younger. In fact the youngest formation seen in the Zion area is the oldest exposed formation in Bryce Canyon - the Dakota Sandstone. There are, however, shared rock units between all three, creating a super-sequence of formations that geologists call the Grand Staircase. Bryce Canyon's formations are the youngest known units in the Grand Staircase. Younger rock units, if they ever existed, have been removed by erosion. See geology of the Zion Canyon area and geology of the Bryce Canyon area for details.
These layers have undergone 5000 to 10,000 feet (1500 to 3000 m) of uplift starting about 65 million years ago with the Laramide orogeny which has increased the ability of the Colorado River to cut its channel to make individual plateaus out of the Colorado Plateaus region. The major canyons of the region did not start to form until about five to six million years ago when the Gulf of California opened up and thus lowered the river's base level (its lowest point).
Reference
- National Park Service: Bryce Canyon National Park Nature and Geology - The Grand Staircase (http://www.nps.gov/brca/geology_grand.html) (public domain text)