The Horseshoe Bend of the Colorado River, downstream of Glen Canyon and Lake Powell near Page, Arizona, marks the spectacular gateway to the Grand Canyon. The sweeping panorama of the canyon, with the Paria Plateau and Vermilion Cliffs in the distance beneath dramatic thunderstorm skies, evokes a profound sense of the wild and unknown.
The formation of this incised meander, a striking combination of canyon and river bend, began about 75 million years ago. During the Late Cretaceous, the age of the dinosaurs, the Colorado Plateau was still close to sea level. Today, it stands about 1,300 meters (4,200 feet) above sea level. The Colorado River cuts through the much older Navajo Sandstone. This rock began forming about 180 million years ago during the Jurassic Period, from windblown sand deposited across an immense desert that stretched from present-day Arizona to Wyoming. The canyon walls expose the sandstone’s characteristic diagonal layers, remnants of the cross-bedded structure of ancient sand dunes.
The Navajo Sandstone is exposed today because younger sediments that once covered it have been stripped away by erosion as the Colorado Plateau rose. Through this gradually eroding landscape, the ancestral Colorado River meandered much as rivers do today. But when the Colorado Plateau began to rise rapidly about 5 million years ago, the river cut deeply and swiftly into the rising bedrock, carving this canyon while preserving the pre-existing 270° bend.
Today, the elevation difference between the rim and the river is about 300 meters (1,000 feet). The Colorado River continues to deepen Glen Canyon at a rate of about 0.007 inch (0.17 millimeter) per year. This may sound negligible, but sustained over 5 million years, it amounts to about 2,800 feet (850 meters), roughly the depth of today’s Grand Canyon. In the distant future, the river may eventually erode through the narrow neck of rock. This could create a natural bridge, which would ultimately collapse and leave behind a butte, like so many others found throughout the Grand Canyon.
The approaching thunderstorm dramatically enhances the sublimity of this landscape. Sporadic flash floods triggered by intense thunderstorm runoff are an important force of erosion in this otherwise arid environment.
