Canals (IMAGE) Penn State Caption The Colorado River canyon, just above Grand Canyon (left), and Nanedi Vallis on Mars (right) pictured at the same scale shows how both canyons were formed by rivers that appear to have been approximately the same width. The river channel on Earth looks darker because it is filled with water, whereas Nanedi Vallis has been dry for billions of years. Credit Sonny Harman/Penn State Usage Restrictions Non commercial use only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.