Photo of the Day 12 July 2008

Grand Canyon National Park, Arizona, 2005
Photograph by Michael Nichols
A pool of rainwater in a Grand Canyon boulder reflects canyon and sky. A writhing giant with scores of limbs (some still unnamed), the Grand Canyon slices 277 miles (446 kilometers) through northern Arizona, extending 18 miles (29 kilometers) at its widest point and 6,000 feet (1,800 meters) at its deepest—one of Earth's largest canyon systems. Cut by the Colorado River in the past six million years, it exposes rock strata that detail nearly two billion years of North America's geologic history.