Arizona is a geological laboratory because the natural forces in play are so visible. Erosion is a general term for the weathering of rocks and the transportation of them. The forces of erosion are gravity, ice, water and wind.
The San Francisco Mountain in Flagstaff is a strato-volcano in the midst of a volcanic field of over 600 smaller volcanos. This largest volcano is now 12, 633 feet in elevation, but it is estimated it reached 16,000 feet before a sideways eruption or glacial erosion, or both, collapsed or carved out the northeastern side of the mountain.
You can see green lichen growing on this large basalt boulder at the base of Mount Elden in Flagstaff. Weathering and erosion from the lichen, rain, snow, and freezing winter temperatures have and cracked the boulder in half.
In the mesa shown below, you can see how the soft sedimentary layers at the top have been weathered away by wind and water and gravity has piled it around the bottom.
Wind is a powerful force in erosion as you can see in the photo of Tsegi Canyon below where it hollows out the sedimentary rock.
Water helps to carry away the debris weathered from the higher elevations and the grit and sand in the water help to erode more rocks as it passes.
The classic Arizona erosion example is the Grand Canyon of the Colorado River.