Geology Bit at the end: Jurassic Entrada sandstone, Dakota formation, erosion & hoodoo creation, the Sevier fault

I woke up in the morning before the sun started to rise and saw that, during the night, another truck arrived, shielding me perfectly from the road. Breakfast was started on the sandy spot where I stood while I admired the red rocks that surrounded me on all sides. I also noticed that I was parked near a bridge—and near a dam- the Glen Canyon Dam that holds Lake Powell and Wahweap Bay in their place.

I strolled over to the dam, then stopped by in Wahweap which was unplanned but worked out perfectly; besides bathrooms where I could brush my teeth and refill on water, they had some pretty gorgeous views of the lands stretching eastward.

I had over 100 miles to go before I’d make it to Zion National Park and no planned stops in between. As it turned out, having no planned stops didn’t mean I’d really make that trip in the two hours my map predicted.

I was still dressed in my pajama pants. They were the comfiest thing and I refused to take them off until it was too hot to do so. When I and many others were stopped for about a quarter-hour because of road construction and my stomach started to demand more food, I hopped out of the car to get to the trunk for some cheese crackers as I was, in said pajama pants. I didn’t think much of it at all and was soon on my way.

I was stopped once more shortly after making it through the construction zone. This time, it was by a sign that announced a hoodoo was nearby. I pulled into the small parking spot and got ready to walk to the Toadstool Hoodoo. A few cars pulled up just as I was about to head out on the short hike, still in my pajama pants.

“Hey! You were in the traffic jam a few cars before us!” a guy hollered from one of those cars. I looked over at him, perfectly confused. “We saw your pajama pants. You ran back to the car when we could finally go.”
“Oh! Yeah, I was getting some snacks. It was a long wait.”
“Sure was. Are you hiking in those?”
“Yeah, I am.”
“Well, enjoy!”
“You too!”

Well, that was a… unique conversation. I headed out to the hoodoo through the mini-canyon. One thought immediately shot through my head: why do they advertise the Toadstool but nobody mentions the ABSOLUTELY RIDICULOUSLY AWESOME SANDSTONE LAYERS?

Like Alice in Wonderland, I walked through the dry riverbed. until I reached the hoodoo. The body of the hoodoo is made of Entrada sandstone while the rock that sits on top of it is of the more resistant Dakota formation. (More geology at the end of this blog post! I don’t want to bore those of you who actually have a life.) And I mean, it was interesting… but what took my breath was the gorgeous red layer of Jurassic Entrada Sandstone that hugged the whole area in its arms.

Looking down the valley, the red sandstone only kissed the tips of the hills while further up, the layer was embedded between grey and beige sandstone like a ribbon tied around a vanilla cake.

A little bit up the tiny valley, more hoodoos sprung up in small groups like mushrooms after rain. Even though there were a few people around, it was easy to feel as if I was there alone: the few visitors, including myself, spread around the place, It was quiet and serene.

Soon, it was time to return, cross the Sevier fault, and head up the gorgeous Grand Staircase toward Zion.

Geology Time!

Get some tea (or beer) and find a comfy seat; this one is going to be fun!

Hoodoos & Erosion

Hoodoos are formations that came into existence thanks to one important process: erosion. They’re also called fairy chimneys, earth pyramids, or tent rocks. They’re made of sandstone and other fine-grained sedimentary rocks and created by uneven weathering and erosion¹.

There’s a slight difference between weathering and erosion: weathering is the processes (both physical and chemical) that break up the rock, erosion is the processes that remove the weathered, broken-down rock.

Jurassic Entrada Sandstone & Dakota Formation

Jurassic Entrada sandstone was deposited some 180 to 140 million years ago in several different environments. Toadstool Hoodoo, as mentioned above, is made of Jurassic Entrada sandstone and Dakota-formation sandstone. The entrada sandstone is way less resistant to weathering than the Dakota-formation sandstone. Therefore, it broke down faster while the Dakota sandstone rock remained more intact, sitting on the top of the spire.

Sevier Fault

The Sevier fault is one of the active faults that work tirelessly to break apart the western margin of the Colorado Plateau. It’s a normal fault; the mass above the inclined fault, the hanging wall, moves downward while the mass below the fault, the footwall, moves up.

The fault elevates the Paunsaugunt Plateau and Bryce Canyon National Park to over 8,000 feet and showcases two main rock types: the igneous black basalt of an ancient lava flow and the sedimentary rocks, mostly pink sandstone.

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Looking for more geology or curious about what happened during the road trip before the strange convo with the guy who noticed my pajama pants? Read here: