Yesterday, I visited the Santa Catalina Mountains near Tucson looking for a little fall foliage color. Unfortunately, most of the deciduous trees were only just starting to change color. These Quaking Aspens (Populus tremuloides) near the summit of Mt. Bigelow were still green with only the faintest tinge of their golden fall colors.
Quaking Aspens are colonial organisms, and a dense stand of these trees may be composed of genetically identical clones sprouting from a shared root system. Because of this, a grove of Quaking Aspens could theoretically be considered a single organism.
Even though the leaves on the Quaking Aspens were still green, I did find some colorful fall foliage, a few reddish weeds like these ones.
The red colors in fall foliage are caused by an interruption in the production of green chlorophyll and the subsequent, stress-induced production of red to purplish pigments called anthocyanins.