Fall colors on aspen trees. Fall - September / October. Temperatures cool down during this period and the lack of wind can make this some of the most ideal weather during the entire year. Summer crowds are gone making it an ideal time to see the monument on your own. This is a good time for backpacking into the wilderness area of the monument. Camp sites are easy to find and water and facilities in the campground are available into October depending on the low temperatures. Aspen in the mountain areas to the north of the monument take on autumn colors during this time.