Grand Canyon NP

On our first fieldtrip, we visited the Grand Canyon, a remarkable assemblage of plateaus, mesas, and buttes of various colors and contours exposed by erosion. The reds, browns, yellows, and maroons reflected off the canyon walls at sunset result from trace amounts of iron and other minerals that impart color to the rock. The many layers of sedimentary rocks were deposited over a period of millions of years. The youngest formation at the top of the canyon walls is the Kaibab Limestone (250 million years old). Older rocks, toward the bottom of the canyon, include igneous and metamorphic rocks, such as Vishnu Schist and Zoroaster Granite (up to 2 billion years old).

Grand Canyon, Arizona from the South Rim
Photograph by Mark Eberle, March 1999

These various rock layers were exposed by the erosional power of water -- the depth of the canyon was cut by the Colorado River, and its width was created by runoff from rain, snow, and tributary streams. The relatively young canyon, estimated to be 5 to 6 million years old, lies within the geological province known as the Colorado Plateau, which is characterized by a series of horizontal rock layers that have been uplifted thousands of meters above sea level. The depth of the canyon reaches over 1,800 m, from rim to river, and its width is approximately 16 km from the South Rim to the North Rim.

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