The Middle Miocene Pyramid Flora of Western Nevada

The Pyramid flora (15.8 m. years) is wholly dominated by broadleaved deciduous hardwoods of eastern alliance that indicate ample summer rain. Deciduous hardwoods are largely absent from slightly younger nearby floras (less than 15.8 m. years) that are dominated by mixed conifer and broadleaved evergreen forest species. The change is attributed to reduced summer rain that reflects global climatic change influenced by spreading antarctic ice.