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Postcards from Pangea. Petrified Logs See the Sky for the First Time in 225 Million Years

Updated: Jul 17, 2021

225 million-year-old trees finally see the light of day in the Circle Cliffs.

The Chinle formation of sandstone is a favorite photographic subject. It is very colorful and easily eroded into lovely forms by erosion. In Grand Staircase-Escalante National Monument, the formation is well exposed in the Circle Cliffs below the vertical red walls of the Wingate formation.

Banded hills of the Chinle Formation in the Circle Cliffs. Photo © Donald J. Rommes.

225 million years ago, in the Triassic Period, the Chinle formed from ancient mudstones and siltstones brought to this area by slow-flowing rivers and streams. At that time, this part of what is now Utah was a lowland at a latitude similar to modern-day Puerto Rico. It was close to the ocean at the western edge of the supercontinent called Pangea and had a tropical environment.

Unmistakably a section of a tree trunk, this piece of petrified wood rests on the the mudstone it was buried under. Photo © Donald J. Rommes.

A forest of large trees grew here. They died, and some fell into the rivers where they underwent a process called permineralization. Waterborne quartz filled the spaces in the wood and often preserved the cellular structure. The organic structure gradually became mineral (“petrified”).

The forest of petrified trees is one of the under-appreciated treasures of Grand Staircase-Escalante National Monument. It is the second largest such forest in this country, second only to the one preserved in Petrified Forest National Park, and one of the largest in the world.

Although the Chinle formation can be many hundreds of feet deep, much of the petrified wood seems to be located in a fairly narrow layer of pink sandstone that was probably deposited by a particular stream. Knowing that, I was attracted by a band of pink sandstone I had noticed in an out-of-the-way area of the Circle Cliffs.

Pinkish band of sandstone in the Chinle formation and scattered pieces of petrified wood. Photo © Donald J. Rommes

I explored the area on several occasions. It took a bit of effort to hike up the Chinle—especially with a backpack full of camera gear. The steeply sloped mudstone had multiple horizontal bands of color and the easily eroded material was cut by frequent gullies. The surface was crumbly, with a popcorn-like texture

The top of the Chinle formation was a divide of sorts—a pass. From there, the land to the west sloped less severely. Dry channels, carved by intermittent rainfall heading west, led to deeper gullies and, eventually, a canyon further down the slope. In some of the deep channels, entire petrified logs are gradually being exposed.

The Chinle Divide, scattered rocks of the Chinle formation, and pink sandstone. A 225M year old petrified tree finally sees the light of day. Photo © Donald J. Rommes.

The petrified wood here, unlike the petrified wood of a similar age in Petrified Forest National Park in northern Arizona, is not colorful but black and shiny. In other places on the Circle Cliffs, pieces of petrified wood—probably originating from the breakdown of larger logs—are scattered over the rounded Chinle hills and glint in the sun like broken glass.

As is so often the case in Grand Staircase-Escalante, I was alone in a colorful place of natural quiet. It was relatively easy to focus on the task of composition at hand. With no distractions, I had the mental freedom to let my mind wander.

Petrified "postcard" from Pangea. Photo © Donald J. Rommes.

As I photographed the petrified logs emerging from their ancient cover, I couldn’t help but contemplate their history. A 100-foot tall tree, standing at the edge of a river near sea level, dies and falls into the water. It is gradually covered by sediment, and then by many hundred more feet of material over the centuries. Tectonic plates shift, continents move, climate changes. Thousands of feet of sand cover the land and gradually turn to stone. An inland sea comes and goes. Dinosaurs appear, dominate the earth for more than 150 million years, and disappear completely after a cataclysm. The land is raised more than a mile above sea level, layers of rock are dramatically tilted, and thousands more feet of overlying sediments are removed by erosion.

Eventually, the process reaches these ancient logs, uncovers them, and exposes them to the sun for the first time in 225 million years.


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