Yellowstone's Petrified Forest

Around 50 million years ago, scientists say this area of the park was flourishing with tall trees when volcanic eruptions buried the forest in ash.
Petrified tree trunk in Yellowstone National Park.

Petrified tree trunk at Yellowstone National Park. by Ildar Sagdejev via Wikimedia Commons

Tucked away on a tall, dusty-brown dirt outcropping in the northeast corner of the park lies a natural attraction just waiting for passerby to take notice.

With a historical story to tell just as the parks other natural wonders do, Yellowstone’s petrified forest is a just as much look into the past as it is something to be admired in the present.

Around 50 million years ago, scientists say this area of the park was flourishing with tall redwood trees, maples, magnolias, oaks, dogwoods, and pines when volcanic eruptions from the nearby Absaroka Mountain range buried the forest in ash.

As the organic, woody material of the trees began to decay, silica-rich groundwater started to seep into the wood cells of the trees. This occurrence helped to preserve the buried forest by literally “freezing” the wood and halting their decomposition.

Meanwhile, the ash exposed on the surface slowly weathered into clay and the clay eventually weathered into soil that was suitable for new forest growth.

This cycle is thought to have taken 200 years – from old to new forest. It was a process, scientists say, that repeated itself for tens of thousands of years.

Glacial ice and the eroding power of running water and wind have uncovered the vast areas of fossil forests that visitors can see today. The Specimen Ridge site has 27 successive layers of forest – tree stumps that stand exposed, stratified from oldest to youngest as you make your way up the hillside. At the 3,400 foot high Specimen Creek formation, there are about 50 successive layers of exposed forest that can be seen.

Some of the oldest petrified trees uncovered by erosion in the park are up to 25 feet in diameter and count up to 1,000 tree rings.

Even more forest still lies fossilizing underground – an unseen natural wonder awaiting the attention of future visitors to Yellowstone.

By April Cumming

Related Story: How Yellowstone's Petrified Forests Were Created