Colorado depends on the quaking aspen tree for its fall color - just that simple. Colorado does not have the multiple colors you will find in trees of many other states. The dominant autumn color is the brilliant golden yellow of quaking aspens mixed with the greens of a majestic coniferous forest.
Because of elevation changes, the peak color season for quaking aspens in Colorado can last from late September through the entire month of October. During that month-and-a-half period you are going to find glorious fall color somewhere in Colorado. Still, at any given location, the color only lasts about a week.
Colorado.com says it best:
The quintessential Colorado tree is, of course, the quaking aspen. We've named towns, streets, dogs, even our beer after this glorious tree. In the summer, the aspens provide shade for our favorite flower, the columbine, and in the fall, Coloradoans rejoice when the aspens quaking leaves turn brittle and gold.
Photo Gallery of Favorite Fall Tree Foliage