<p>Fossil redwood tree trunk in the Eocene of Wyoming, USA.
</p><p>This is a scarce example of a still-standing, Eocene-aged fossil tree in Yellowstone Park, Wyoming.  The tree itself is a redwood, probably belonging to the genus Metasequoia.  Redwoods do not live in Yellowstone today, so the climate has clearly changed since the Eocene.
</p><p>The fossil wood has been permineralized.  "Perminerlization" is the proper term for what most people called "petrified wood".  Permineralization involves the precipitation of minerals (usually quartz - SiO2) in the porosity of wood or bone by groundwater that has percolated through.  The original microscopic-level anatomy of wood can be preserved in a permineralized fossil.  Sometimes mineralization can completely obscure the biologic structure of fossil wood - some paleontologists refer to that as quartz replacement, but it's just extreme permineralization.
</p><p>Classification: Plantae, Pinophyta, Pinopsida, Pinales, Cupressaceae
</p><p>Stratigraphy: Sepulcher Formation, Washburn Group, lower Absaroka Volcanics Supergroup, Eocene
</p>
Locality: "Petrified Tree", northern Yellowstone National Park, nw Wyoming, USA
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/13460816034/">Fossil redwood tree trunk (probably Metasequoia) (Sepulcher Formation, Eocene; "Petrified Tree", Yellowstone National Park, Wyoming, USA) 1</a>