Notice how canyons through the Grey Cliffs are wider, meander more, and aren't as deep as those through the White Cliffs? The difference is the presence or absence of flash flood erosion. Even though the White Cliffs are composed of more durable rock than the Grey Cliffs, they still erode at a faster rate! Just as geology influences plants, plants control geology. Ponderosa Canyon is so named because of the huge Ponderosa Pines on the canyon floor. Some of these trees measure more than 5 ft. in diameter and exceed heights of 150 ft. However from high above at the viewpoint you would never know this. In fact many are confused by the name, not expecting to find themselves surrounded by a forest of Blue Spruce and Douglas-fir. Certain types of vegetation grow in certain environments according to conditions such as moisture and temperature. These conditions are strongly controlled by elevation. Forests, therefore, are divided into zones or forest types according to elevation, because a forest's dominant tree species varies with these changes in elevation.