Into the Great Unknown: The Aftermath of Chaos...Finding Beauty in the Oldest Rocks of Grand Canyon

If you've been following the story so far, you will know that we reached day nine on our rafting journey through the Grand Canyon, and that day nine was a bit of a disaster for yours truly. Our raft had flipped in Crystal Rapid, the worst rapid on the river, and I took a very long swim in frigid turbulent water before being plucked out by my guardian angels (Barry, Bev and Jeff). We made it through eight more rapids that day without incident, and made camp at a narrow strip of sand called Hotauta.

As I noted in the previous post, my camera was badly damaged (I had a spare in storage), and my trip journal was soaked. I spent the evening carefully separating and drying the pages, hoping that I could recover most of them. I also had to deal with the psychological aftermath. Being in an unexpected ride down a violent river without my boat might be an expected part of river running (and certainly no one was saying it was an easy thing to do), but I'm a desk-bound professor most of the time. This was something very new for me.

The best thing I could imagine would be to have a peaceful and serene day on the river, and the Colorado seemed to understand this: there were ten rapids in our path on day 10, but only one of them, Walthenberg (6) was greater than 5 on the rapids rating scale. And it came early in the day. We had three excursions planned in the side canyons, and they sounded like wonderful places.

It seemed a good sign to have a big Swallowtail Butterfly land on my gear as we were loading the rafts. It seemed a bit disappointed that my bag wasn't the biggest darn flower ever, but it hung around long enough to get a picture.

We went through the first two rapids, Bass and Shinumo, and pulled out at Shinumo Creek.

The walk was short, but quite interesting, as the creek filled the canyon bottom. I was absolutely sure I was going to slip on the muddy rocks and destroy my remaining camera. But it was just beautiful, and the fifteen foot waterfall was a refreshing retreat from the hot sun.

We headed back onto the river, and soon passed the creatively named 113 Mile Rock, an outcrop of schist that practically blocked the river. It also marked the halfway point in our 226 mile trip (it was day 10 of 16, so our average daily mileage was going to increase).

Since Walthenberg Rapid, we had been traveling through the oldest rocks to be found anywhere in the Grand Canyon region: the Elves Chasm Gneiss, dated at 1.84 billion years. These rocks may represent the ancient crust on which the other metamorphic rocks were emplaced many tens of millions of years later. I hate to say it, but I was distracted that day and didn't realize that we were passing through these rocks until a day or two later when I retrieved my geologic map out of the luggage. But I managed to snap a number of pictures because the rocks were intriguing to look at whether I knew their age or not.

 In many places the rocks are intruded by pink dikes and veins of granite pegmatite, a rock with exceedingly large crystals of feldspar, quartz, and muscovite mica (above). In a few places I could make out darker intrusions that looked like basalt (which is youngest in the picture below: the black or the light colored intrusions?)

 Before Glen Canyon dam was built the Colorado River carried an incredible amount of silt and mud. According to some sources, when the river used to run at 100,000 cubic feet per second, half of what flowed down the river was sediment (Death in the Grand Canyon by Ghiglieri and Myers). The sediment gives the river the tools needed to sculpt the incredibly hard rock, and we passed numerous beautiful exposures of intricately shaped gneiss, schist and granite.

We were still in the Granite Gorge, but we noticed that the inner canyon wasn't as deep as it had been, and we started to see Tapeats Sandstone in the cliffs not too far above us.

As we neared Elves Chasm, the Tapeats was at river level, and we were treated to an exposure of the Monument Monocline in the sandstone layers. A monocline is a fold in the rocks that looks like a carpet thrown over a step: level horizontal rock, then a flexure as the rock bends downward, and then horizontal layers again. They tend to occur when a fault fractures harder rocks at depth, but only bends the sedimentary layers above.

The folds were an unexpected sight. So were the travertine deposits that were exposed along three miles of the river starting at Mile 116. Travertine is generally composed of calcium carbonate (the mineral calcite) which was leached out of the overlying Redwall, Temple Butte, and Muav formations and deposited by springs in the Bright Angel Shale. The travertine completely covered the Tapeats in places, including the area around Elves Chasm.

What is this "Elves Chasm" that I keep mentioning? It was our next stop, but that will be in the next post!

Not all the Rocks in Grand Canyon are Flat...

It is sometimes too easy to fall into a perceptual trap when confronted by a place as amazing as the Grand Canyon. The Spaniards who first saw the canyon in the 1500's thought it was maybe a thousand feet deep, and the Colorado River only 6 feet wide. Going from viewpoint to viewpoint, one might think that the layers of the canyon are uniform...and flat.

There are some important exceptions, which to me is what makes each viewpoint unique and interesting. For instance, if you walk to the east from Grandview Point, you can catch the Sinking Ship, and see that large structures offset or bend the Paleozoic layers of the canyon. This is an example of a monocline: a fold in which sedimentary rocks are draped over a fault like a rug thrown over stairsteps. This is part of the Grandview-Phantom Monocline. It formed in the late Mesozoic Era (the dinosaurs) during a regional disturbance of the crust called the Laramide Orogeny. The orogeny also produced the Kaibab Plateau, the highland through which the Grand Canyon was carved.

Wi-fi is tricky when camping. I think the McDonalds crew wants me to vacate our table...we've been here an hour, and we have to hit the road anyway. Until next time!

Vagabonding across the 39th Parallel: Having a "Swell" Time on the Reef!

If you thought I was talking about sipping pina coladas on a beach in the Caribbean, well, think about nearly polar opposites. Hot, yes, but not tropical. We were in a very dry and remote place in central Utah. This is a continuation of our July journey through the American West, vagabonding across the 39th parallel. The swell is a huge domal uplift, and the reef is a long monocline. If there is one thing to say about driving along the 39th parallel, it is that the landscape never stays the same for very long.

Having crossed the transitional zone of the Wasatch Mountains, we had left behind the Basin and Range Province, and were now on the relatively stable crust of the Colorado Plateau. The plateau, as the name suggests, is mostly made of high flat mesas and buttes of horizontal sedimentary layers representing some 500 million years of earth history (with much older stuff buried beneath). Although mostly flat, the plateau region has been faulted here and there, and in places has been warped into a series of basins and broad domes. The San Rafael Swell is one such dome, and it is huge, 130 miles long and 70 miles across. From space, it is one of the most obvious structures in all of Utah (above).

A dome in this case refers to the shape of the sediments. They've been pushed up like a blister, but erosion has sheared off the upper layers, exposing the older layers underneath. As we left Salina, heading east on Interstate 70, the signs noted that there would be no services for the next 100 miles. That is the kind of sign that makes you look at the temperature and gas gauges...

At least the road was not as lonely as some of the others that we had been traveling. And because of the beautiful scenery, there are a number of turnouts with nice photo opportunities. The rocks are striking. They represent the entire Mesozoic Era (the age of the dinosaurs, basically), which lasted from 245 to 65 million years ago. Upper Paleozoic rocks are exposed in the core, while early Cenozoic rocks are found around the margins of the dome. All in all, some 8,000 feet of sedimentary layers can be seen while crossing the San Rafael Swell (the Grand Canyon has only 4,000 of Paleozoic layers, in comparison).

At the top of the post, I said we weren't on a tropical beach. That's not entirely true, it's just that the timing is off a little bit. Some of the oldest rocks exposed on the Swell were deposited on a tropical beach, and we had arrived just 300 million years too late to listen to the crashing waves.

The road passes through an hour of horizontal Permian and Triassic rocks, but at the eastern end of the Swell, the landscape goes crooked. The margin is marked by a massive monocline, an odd fold that has flat layers on one side, a flex in the middle and flat layers at a lower level. The effect is something like a stack of rugs draped over a step. We had reached the San Rafael Reef.

I know this photo below looks cockeyed, but if you look at the telephone poles on the ridge line, you'll realize the camera was level. It was the landscape that was bent. These monoclines were called reefs because they were barriers to east-west travel, just as a coral reef can block access to a harbor. Resistant sandstone layers eroded into teeth-like spikes separated by narrow slot canyons that made passage difficult. The freeway could only be constructed here by blasting a passage through the rock (if you click on the opening photo, you can see the cut at the bottom, with a red car for scale).

I heard braying while exploring the last rest stop, and saw a small herd of wild burros in the canyon below.

I pulled over as we passed the base of the monocline, and got some shots of the reef looking off to the south. One can see how difficult it might have been to find a passageway for a wagon or a Model T. The jagged white rocks are the Navajo Sandstone, the remains of a vast Jurassic dune sea that covered several states (the Navajo forms the cliffs of Zion National Park).

I've heard there are some nice canyons to explore in the area, as long as it is not raining. The slot canyons are notorious for trapping hikers.

The monoclines and domes of the San Rafael Swell were formed by compression of the crust, which was related to the Laramide Orogeny that took place around 80 to 50 million years ago. This event also had a lot to do with the formation of the Rocky Mountains. The monocline hides a large thrust fault in the deeply buried ancient crust, but the overlying sedimentary layers folded rather than split when the fault was active.

At the base of the reef, horizontal layers appeared again, including the very colorful Morrison formation, the one made famous by the many discoveries of dinosaurs, including the huge brontosaurs (yes, I know they aren't really called that), the allosaurs, and stegosaurs.

A few minutes later we arrived at the settlement of Green River (population 600 or so) to look for lunch. We decided not to eat at the "Rant Lounge", and settled instead for Arby's.