On a drive from Taos to Cortez, CO, we managed to just about hit the peak of autumn color for the Aspen trees. Why are they called Quaking Aspens?
The aerodynamics of Aspen leaves cause them to flutter and shake when the breeze blows. The base of the leaf is very flexible, allowing the leaf to bend first one way, and then the other.
In addition to being a beautiful sight, this quaking also makes a wonderful sound, almost like rushing water.