Here's why:

* Erosion: The primary force behind the Grand Canyon's creation was erosion, primarily caused by the Colorado River. Erosion is the process of wearing away and transporting rock and soil, which is a destructive process.

* Uplift: While the Colorado River carved the canyon, the uplift of the Colorado Plateau provided the elevation difference that allowed the river to cut so deeply. This uplift was a constructive force, but it was the subsequent erosion that created the canyon itself.

So, while uplift played a role in setting the stage, the erosion that shaped the Grand Canyon is the defining destructive force.