Thursday, December 24, 2015

Petrified Forest National Park

Back in the beginning of March, I traveled out West with Ohio University Outdoor Pursuits on a Spring Break trip. The OU Outdoor Pursuits is a department within the Division of Student Affairs at Ohio University which focuses on outdoor adventure and recreation trips. They offer us students an extremely affordable and guided way to travel to new, exciting places and do things like backpacking, rock climbing, hiking, and more.

I've been sitting on my Spring Break trip photos for months and months now, and I've finally decided to get myself in gear and write about it! The main point of the trip was to visit Mammoth Cave National Park and the Grand Canyon National Park, but due to some unforeseen circumstances and flexibility Outdoor Pursuits decided to add a few other national parks on the fly, one of which was Petrified Forest National Park. I'll be making a really big post chronicling the whole trip soon, but for now I'd like to focus on Petrified Forest.

Petrified Forest shrub steppe
We arrived at Petrified Forest National Park on March 1st, 2015. This National Park is located in east-central Arizona. It straddles Interstate-40, a beautiful highway which we traveled nearly 500 miles on. We were all a little stir crazy from being on our two minibuses for about 980 miles straight, and when we pulled into the park we were all ready to see something amazing. The group leaders decided to take the auto-tour of the park, and upon getting onto that park road we were met with the sight above. This is a beautiful semi-desert shrub steppe; at least, I thought it was beautiful. Many of the others thought it was a bit lackluster. But then we rounded a small hill....

Petrified Forest Painted Desert
The view from Tiponi Point. We actually visited on a rare day with rain showers, which you can see in the photo above.
....And the Painted Desert appeared. Various sounds of awe emanated from everyone, and we all stared at the mesmerizing sight before us. As someone who had never been west of Ohio up until this point, I cannot even begin to put into words how I felt when this view appeared. The Painted Desert is a relatively small desert, clocking in at only about 120 miles long and 60 miles wide. As you might guess, the colorful rock formations are the reason behind the name. The Painted Desert is located in the southern portion of the Colorado Plateau, which is a large uplifted region that lies in parts of Arizona, Utah, New Mexico, and Colorado. The very southern tip of the Painted Desert makes up the more northerly half of Petrified Forest NP.

Petrified Forest Pilot Rock






















We began our tour in the northern portion of the park. Most of the landscape in Petrified Forest National Park is an example of badlands. Badlands form when soft sedimentary rocks are heavily eroded by water and wind. The best known example of badlands is Badlands National Park in South Dakota, but they occur throughout the world. In the case of Petrified Forest, these badlands are made primarily from layers of soft siltstone, mudstone, and shale. The vast majority of rocks exposed at Petrified Forest belong to the Chinle Formation, a formation which dates to the late Triassic. Select areas of the park also exhibit rocks from the Bidahochi Formation. This formation was formed from a mix of lake and volcanic sediments, but most of it has eroded from the park. Pilot Rock - which is the large, shadowy hill looming on the left side of the horizon in the photo above - is, for example, capped by rocks of the Bidahochi Formation.

Petrified Forest Chinde Mesa
The Chinle Formation is broken up into several sub-units that are called members. Four of these members are exposed in Petrified Forest NP. In the northern Painted Desert section of the park, one can see two members. Essentially everything you see in the photo above are rocks belonging to the Petrified Forest Member of the Chinle Formation. This member consists primarily of siltstone and mudstone, both of which are types of very soft sedimentary rocks. There are a few layers of harder sandstones here and there as well. Also visible in this particular region is the Owl Rock Member. If you look at the horizon toward the center-right in the photo above, you can see a much taller hill called Chinde Mesa. Chinde Mesa is capped by Owl Rock Member layers, while most of the Owl Rock Member has been eroded away elsewhere in the park.

Petrified Forest Black Knoll
As you travel southward through the park, the reds of the Painted Desert fade to various other colors. The view above is from one of the overlooks on a formation called Blue Mesa. These rocks are still part of the Chinle Formation, but belong to a different member called the Sonsela Member. The hill in the background along the horizon is called Black Knoll. Black Knoll doesn't belong to the Chinle Formation, and instead is actually made of hardened basaltic lava. This lava was laid down in the late Cenozoic Era, about 5-1.4 million years ago. The Cenozoic Era is the era after the dinosaurs (the Mesozoic). As I mentioned earlier, the majority of rocks found at Petrified Forest date to the Triassic Period, which is the earliest period of the Mesozoic.

Petrified Forest Blue Mesa Member

Below the Sonsela Member is the Blue Mesa Member. This member is filled with stunning purple hues, as you can see above.

Petrified Wood
Now we are going to get to the namesake of the park. This is a chunk of petrified wood. Petrified wood is a type of fossil formed through the permineralization of wood. Essentially, a dead tree will fall and be quickly buried by sediments. Water containing a large amount of silica will then seep into the ground and begin to seep into the log. Slowly this silica-rich water will then begin to replace the wood as the wood decays. This replacement process takes place at the cellular level, with cavities and other parts of the cells being filled or replaced by minerals. What is left is a fossil in which all the organic material has been replaced by inorganic minerals.

Petrified Forest petrified log
As you might have guessed, there's a lot of petrified logs within the park. A "petrified forest," if you will. To understand why this is, one must go back over 200 million years ago. During the late Triassic, this land was situated near the coast of the super-continent Pangaea. This region was a wet location back then, with major rivers meandering through the area and emptying into the nearby ocean. All of the land in the park was river floodplains and bottomlands. These floodplains and bottomlands were covered in a tall coniferous forest. These tall conifers would die, and sometimes one would fall in the rivers. The rivers would transport them downstream where they would get snagged on rocks or each other, and they would end up being buried by the river sediment and often become petrified. Occasional nearby volcanic eruptions would also knock down trees and cover the land in ash, a perfect medium for petrification to take place. Over hundreds and thousands of years, thousands of logs were fossilized and preserved, causing the land to be littered with petrified logs nowadays. As erosion continues, more and more logs are uncovered. The trees that lived here in the Triassic would have reached upwards of 200 feet in height, but you don't see chunks of petrified wood that long. Oftentimes the pieces are only a few feet long and look like they've been chopped in pieces, like the petrified log pictured above. This is due to past stresses fracturing the logs. The Colorado Plateau experienced millions of years of uplifting, which slowly bent the rock layers. These petrified logs were forced to bend as well, and there would come a point where they simply broke into pieces to relieve that stress.

Petrified Forest Yardang
Since we're on the subject of smaller things within the park, I'd like to talk about this interesting rock above. This is an example of a yardang. Yardangs are streamlined rock formations that have been carved by the wind. Yardangs tend to form in very dry climates (mostly deserts) that experience a strong prevailing wind for most of the year. Bits of sand and silt get picked up by this wind and get blown repeatedly into a rock. Over time this wind erosion eats away at the rock, leaving a long-but-skinny rock formation.

Twin Buttes Petrified Forest


No matter where you go in the park, there's always something magnificent to see. In this photo, the so-named Twin Buttes soar out from a vast, flat steppe that begins when the badlands end. Petrified Forest National Park is an amazing park, but one that doesn't seem to be talked about much. If you're ever out in the area, pay a visit!

Thanks for reading, and stay tuned for more posts from out West!

2 comments:

  1. Not sure I agree with your comment about the Parks' formations belonging to the earliest Triassic period. The formations are all Chinle and they are late Triassic.

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    1. You are correct in that, which is why I believe you might have read my sentence incorrectly. "As I mentioned earlier, the majority of rocks found at Petrified Forest date to the Triassic Period, which is the earliest period of the Mesozoic." The Chinle Formation belongs to the Triassic Period, and the Triassic Period is the earliest period of the Mesozoic. Previous to that sentence I wrote that "The vast majority of rocks exposed at Petrified Forest belong to the Chinle Formation, a formation which dates to the late Triassic." That matches what you said, so I think you accidentally flipped what I wrote (which is something I do all the time!).

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