Stefan Skrobisy, age 14, of Sierra Vista, Ariz.., For his question:

How long did it take Mother Nature to make Grand Canyon?

Grand Canyon was started by forces of nature that began to operate some 50 million years ago. At that time, the Colorado River spilled down the western slopes of gentle hills. Then the ground began to rise, for the massive Rockies were growing. The western slopes became steeper, and many rivers turned around to find easier courses. But the Colorado did not change its course.

The steep slopes made the stream run faster and gave it more energy. As the mountains rose, the river dug a channel. As the Rockies grew, the river became deeper and its banks became steeper. The rushing river took some 50 million years to dig the deep ditch we call Grand Canyon.