Colorado River may have pooled and spilled over to form the Grand Canyon, solving a long-standing mystery ‪—‬ but not everyone agrees

A series of flat red plateaus with a blue river cutting between them, creating a valley, with trees in the foreground. .

The Colorado River may have carved out the Grand Canyon after pooling as a giant lake in what is now northern Arizona and spilling downstream, a new study suggests.

Scientists found that tiny sediment grains in the Bidahochi Basin, upstream of the canyon, were carried from the upper Colorado River watershed by 6.6 million years ago.