The river used to take a little different path every year to erode the bottom of the canyon in more of a flat manner. The Army cane in a planted 100s of Cottonwood trees to "stop the erosion". What it ended up doing was to cause the river to erode huge ditches making it very difficult for the inhabitants to navigate down there with their vehicles. The trees all turn colors in the Autumn causing the bottom of the canyon to "glow" when you are down there. The yellow trees light up against the purple canyon walls creating a gorgeous and wonderful marriage of light and color.