~30 million year old leaf impression fossils of plants from the Rujada Flora from a forest roadcut through the Fisher Formation near Cottage Grove, Oregon. Specimens include leaves of sumac (Rhus varians), alder (Alnus carpinoides), tanoak ( Notholithocarpus simulans), and dawn redwood (Metasequoia occidentalis)!
The Oligocene (~30 Ma) Rujada flora (42 spp.) and the nearby Willamette flora (40 spp.) are dominated by oak (Quercus consimilis) and alder (Alnus heterodonta). The occasional fossil salamander (Palaeotaricha oligocenica) and caddis fly cases of Metasequoia needles (ichnogenus Folindusia) have also been collected in the area.
These leaves fell into and were preserved in an ancient lake. Burial in lake sediments inhibited the decay of organic carbon in the leaves, which makes for exceptional preservation today. A recent roadcut exposed these ancient rocks. Thanks!
The study of paleobotany can help us understand how plants adapted to climate change millions of years ago, which can inform our predictions of how plants today may respond to modern climate change.
Planetary Soils 