The Colorado Plateau:
The Colorado Plateau is an elevated, mildly folded and faulted physiographic province generally underlain by nearly flat-lying sedimentary rocks.

Metamorphic Foundation:
The sculptured beauty and brilliant colors of the Colorado Plateau's sedimentary rock layers have captured the imaginations of countless geologists. This is a vast region of plateaus, mesas, and deep canyons whose walls expose rocks ranging in age from billions to just a few hundred years old. Ancient Precambrian rocks, exposed only in the deepest canyons, make up the basement of the Colorado Plateau. Most are metamorphic rocks formed deep within the Earth while continental collision on a grand scale produced the nucleus of the North American continent well over a billion years ago.

Igneous Rocks:
Igneous rocks injected millions of years later form a marbled network through parts of the Colorado Plateau's darker metamorphic basement. These deeply-formed rocks were uplifted, eroded, and exposed for eons. By 600 million years ago North America had been beveled off to a remarkably smooth surface. It is on this crystalline rock surface that the younger, more familiar layered rocks of the Colorado Plateau were deposited.

Sedimentary Rocks:
Throughout the Paleozoic Era, the Colorado Plateau region was periodically inundated by tropical seas. It was not until the upheavals that coincided with the formation of the supercontinent Pangea began about 250 million years ago that deposits of marine sediment waned and terrestrial deposits dominate. The Mesozoic Era sedimentary deposits are striking. Great accumulations of dune sand hardened to form sweeping arcs in cross-bedded sandstone. Eruptions from volcanic mountain ranges to the west buried vast regions beneath ashy debris. Short-lived rivers, lakes, and inland seas left sedimentary records of their passage.

Miocene Uplift:
Beginning about 20 million years ago, during the Miocene Epoch the Colorado Plateau region was uplifted as much as 3 kilometers. Great tension developed in the crust, probably related to changing plate motions far to the west. As the crust stretched, the Basin and Range Province broke up into a multitude of down-dropped valleys and elongate mountains. Yet for some reason not fully understood, the neighboring Colorado Plateau was able to preserve its structural integrity and remained a single tectonic block. Eventually, the great block of Colorado Plateau crust rose a kilometer higher than the Basin and Range.

Carving the Land:
As the land rose, the streams responded by cutting ever deeper stream channels. The most well-known of these streams, the Colorado River, began to carve the Grand Canyon less than 6 million years ago. The forces of erosion have exposed the vivid kaleidoscope of rock layers that make the Colorado Plateau a mecca for rock lovers.



-- Excerpt from:
USGS/NPS Geology in the Parks Website, 2001