The aspen trees that you see in Tahoe are called Quaking Aspens. They get their name from the way their flat leaves and lengthy stalks tremble in the lightest of breezes. Aspen leaves turn vibrant yellow due to a decrease in photosynthetic activity as the days get shorter in the fall, causing the green hue to fade as chlorophyll production is stopped. Aspens are also the most massive organism on Earth.