English: This natural-colour image of the lower reaches of Big Thompson Canyon illustrates two of the three natural factors that contributed to the flood’s severity: steep terrain and sparse vegetation. Evergreen forests of Douglas fir and Ponderosa pine manage to grip some of the steep slopes, but in many places—most of the northern wall of the canyon, for example—there is little soil or vegetation to absorb or slow the flow of water. The steepness of the terrain is emphasized by the deep shadows that darken north- and north-west-facing slopes. Winter snow still dusts the mountainous landscape.