Grand Canyon

The Grand Canyon, located in Arizona in the United States, is usually regarded as one of the world's seven natural wonders. The canyon, carved [Page 617]by the Colorado River and home to many ecosystems and artifacts, still has scientists wondering exactly how and when it was formed. Each year, nearly 5 million people visit the Grand Canyon.

The canyon is expansive, stretching 277 miles from Lake Powell at the Utah-Arizona border down into Lake Mead, near Las Vegas. The canyon is 6,000 feet at its deepest point and 15 miles across at its widest point.

The wildlife and plant matter found within the Grand Canyon are diverse, attributed in large part to its size, depth, and variation. While the Grand Canyon is very large and wide at some locations, its range of height and size vary along its course and its weather is diverse. Weather varies as much as 5.5 degrees Fahrenheit with each 1,000 foot change in elevation. At certain points, then, the temperature may vary an average of 33 degrees from the upper rim to the river walls. These weather variations allow for the presence of five of the seven life zones and three of the four desert types in North America. The five life zones represented are the Lower Sonoran, Upper Sonoran, Transition, Canadian, and Hudsonian.

The origin of the Grand Canyon is still something of a mystery. Scientists continue to study and hypothesize about its age and origin, but cannot come to a consensus. Despite agreement that the layers of granite at the deepest portions of the gorge are 1.7 billion years old, it is widely accepted that the canyon itself is nowhere near as old.

Figure: The Grand Canyon in Arizona. Layers of the Grand Canyon were formed over a period of about 2 million years

Source: The National Park Service.

Modern geologists are puzzled by the seemingly faster erosion in some portions of the canyon than others. This may be explained by the most widely accepted theory of the canyon's formationthe upper sedimentary layers were the base for several small shallow lakes that existed for hundreds of thousands of years. Over time, the rock rose through tectonic forces to create the Colorado plateau. All the while, the Colorado River cut down through the rock, but was thwarted by the harder portions of igneous rock, which now are some of the narrowest portions of the canyon. This whole process was said to have begun about 70 million years ago. Some researchers argue, however, that the landscape of the canyon is far too immature and must be newer than 5 million years old.

Yet another theory suggests that two separate river systems, not lakes, existed and merged to form what is now the Colorado River. They speculate that the westward river absorbed the eastward river in a process called headward erosion. This theory suggests that the headward erosion process would have begun about 15 million years ago.

Some of the most recent research suggests that the gorge may have been carved within the past million years. Scientists suggest that it was only recently that we have understood just how quickly erosion can take place, drastically affecting the timeline of the creation of the canyon.

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