Into the Great Unknown (Redux II): Journeying to my Roots, and to the Roots of Mountains

I was going over some of my old posts about my journey on the Colorado River in 2013 and came across this personal favorite, a post that discussed my own journey into geology back in 1976 during an earlier adventure of discovery in the Grand Canyon, on foot. It also included some of the most beautiful and dramatic rocks I have ever encountered. From August 30, 2013:

The photo above is my favorite self portrait from my journey down the Colorado River, into the Great Unknown. It's true that I appear in only a half dozen of my two thousand pictures from the trip, but this one captures best the sense of wonderment that I felt during the entire 227 mile long boating adventure. It was taken on one of the really special days of the trip, when we reached the ancients roots of a massive mountain range that today is long gone. It was also a day when I explored the roots of my own life adventure as a geologist and teacher.

And a day when I started to pay really close attention to the rapids on the river.

As a passenger on a raft (really, only a fool would allow me access to the oars in any rapid bigger than a riffle), we trust the boatmen. They are the ones who can quickly read and assess a rapid, either by standing up and observing just before entering, or by pulling ashore and scouting from above. They are the ones who make the snap decisions in the midst of chaos, deciding in an instant whether to pull left or right to get by the unexpected hole or pourover or eddy wall. They are the ones who keep their cool when the giant waves threaten to completely envelop the raft and sometimes tip it over (flipping is a highly undesirable outcome in a rapid; there's nothing fun about it at all). We trust them, and when they do their job really well, a passenger can actually become a bit complacent. If we've managed 40 or 50 rapids without problems, well, it can't really be that hard can it? And that's when things can get dicey.

Passengers play an important role in the run of a rapid, so we have to be paying attention as well. It's hard to imagine that pulling the oars makes any difference in the chaos of a rapid, but it does make a big one. Inches sometimes count. And when the raft threatens to flip over, the passengers have to be thinking fast enough to "highside", to fling themselves towards the rising side of the boat during a tip-over, using their weight to hopefully push the boat back towards the horizontal.

Why was I suddenly watching rapids with a renewed interest? We had reached the point on the river where John Wesley Powell was inspired to write one of his most famous passages, the one which also inspired the name of this blog series:

We are now ready to start on our way down the Great Unknown...We are three quarters of a mile in the depths of the earth...We have an unknown distance yet to run, an unknown river yet to explore. What falls there are, we know not; what rocks beset the channel, we know not; what walls rise over the river, we know not.

The next morning he adds:

At daybreak we walk down the bank of the river, on a little sandy beach, to take a view of a new feature in the canyon. Heretofore, hard rocks have given us bad river; soft rocks, smooth water; and a series of rocks harder than any we have experienced sets in. The river enters the granite!

We can see but a little way into the granite gorge, but it looks threatening.

He and the mountain men who served as his crew had already been on the the river system for two months, and with their inadequate clumsy boats had run or portaged many dozens of rapids that were terrifying. They were running very low on food (the diet: unleavened flour, dried apples and rancid bacon). And now the nature of the rocks exposed along the river promised rapids far worse than any they had encountered upstream.

Why were the rapids worse?

Indirectly, it was indeed the harder rocks. They were entering a part of the canyon composed of harder rocks than anywhere else along the river. It isn't the rocks themselves that make bad rapids, though. The river does not fall over ledges and waterfalls. Rapids on the Colorado River happen because of debris flows that enter the channel from the small tributary canyons. The debris in essence dams the river and forces the river channel to the side, making the cross-sectional area of the channel much smaller. Since the same amount of water in a river passes a given point in a given amount of time (cubic feet per second is one measure), the river must speed up to pass the barrier. You can see this effect in the picture above in Nevill's Rapid.

The severity of a rapid is determined by the volume and size of the boulders in the debris flows, and canyons cut into harder rocks produce larger boulders. Sprinkling a few giant boulders throughout a rapid turns a riffle into a terrifying roller coaster ride.

So that was the day we were facing. We would be entering the Granite Gorge of the Grand Canyon for the first time, and we would now need to run a gauntlet of the biggest rapids to be found on the entire river. It started with Hance (8 on a scale of 10), Sockdolager (7), and Grapevine (7). The next day would include Horn Creek (9). The day after that, Granite (8), Hermit (8), and the ultimate rapid, Crystal (10). These would be followed the same day by the seven rapids of the gemstones (Agate, Sapphire, Turquoise, Emerald, Ruby and Serpentine, ranging from 5 to 7). And 70 miles downstream (with plenty more rapids in-between) Lava Falls (10) awaited our arrival.

We came around a bend in the river, and I encountered a familiar sight in the midst of the Great Unknown. I had been here before! Not on a river rafting expedition, but on a backpacking trip in 1976. It had been one of the most important events in my young life, because it was the trip that set me on the road to becoming a geologist and teacher.

Geology of the Grand Canyon was actually one of the more difficult courses I had ever taken because not only did we need to master a lot of geology in a short time, but we also had to prepare for a challenging backpack down and then back up a series of officially unmaintained trails in the canyon (the New Hance and Grandview trails). The co-requisite for the class was a 2 unit physical education course in backcountry camping that including an entirely separate shakedown trip in the mountains of Southern California. When I came out of the Grand Canyon six days later I knew what I wanted to do with my life.

Of course, a few things have changed since 1976. Geotripper weighs, um, a lot more than that gawky teenager on the right in the picture below. Picture quality has improved, not so much because of better photographers, but it used to be expensive to take and develop pictures, so we never took very many. Plus we were using the old Kodak Instamatic cameras or something similar.

Still, seeing these pictures a few years ago on Facebook (thanks to J. Elson) brought a shock of memories, and now for the first time in forty years I was once again standing at the rapid that made a geologist out of me.

Only this time my mind was on other things. Back then when we finished, we turned around and started hiking back out of the canyon.

We were about to run a major Grand Canyon rapid in boats that suddenly seemed really small. Just like these river rafters in 1976. I noticed that the two biggest boulders haven't moved, and that the rapid was as chaotic looking as ever.

We had reached the base of the Grand Canyon Supergroup, and could now see the three formations that make up the oldest units: the Shinumo Quartzite, the bright red Hakatai Shale, and the basal Bass Limestone (intruded by basaltic dikes). The rocks are tilted about 15 degrees, giving the illusion that the river gradient is even steeper than it already seems. It can't have been a comforting sight to Powell and his men in 1869.

The Grand Canyon Supergroup sits on a mountain range of Andean proportions. Or more properly stated, the layers were deposited on the low erosional plain left behind when a mountain range of Andean proportions was completely washed away. The black schists and reddish granite intrusions once lay some five miles deep in the crust, and now they have been laid bare by the cutting of the Grand Canyon.

The rocks today are called the Granite Gorge Metamorphic Suite, and they formed in a series of collisions between a group of volcanic islands (called terranes), and the ancient North American continent around 1.7 billion years ago. The metamorphic schist and gness units were intruded by granitic magmas at intervals between 1.7 and 1.4 billion years ago. And now those rocks are exposed in the very deepest part of the Grand Canyon.

We successfully negotiated Hance Rapid (not without getting positively soaked), and looking back upstream, I could see the basalt dike that I had found so utterly fascinating on my first trip into the canyon.

The canyon was dark, but I did not feel as sense of brooding. I was exhilarated, my imagination seeing the peaks and canyons that must have existed here in the distant past, mountain slopes which would have been utterly lifeless and barren. Deep gorges must have been cut by rushing rivers that were never seen by any living thing. Entire Grand Canyons could have been carved here and we will never know of their existence. We now entered a fascinating world of exceedingly rugged vertical canyon walls. The silt and sand polished the hard granite and metamorphic rock.

Sockdolager Rapid (the word is an archaic term for knockout blow in boxing) was a fun ride, nothing like the terror-filled lining and portage in Powell's writings.

It was hard to find a spot to scout, so the boatmen checked out the rapid by standing up as they approached.

Between rapids the river was calm, and the canyon walls rose straight from the water.

The metamorphic suite was composed of the most diverse and beautiful rocks that I had seen anywhere on the trip. The polishing simply added to the beautiful sculpted appearance of the rock.

We arrived at camp in Cremation Canyon by 2:30. We had pulled in early because we would be saying goodbye to three of our fellow travelers who would be hiking out of the canyon from Phantom Ranch, and meeting three others who would take their place for the remainder of our journey.

I turned in early once again...tomorrow we faced the biggest rapids so far on the trip.

It's Not What's There in Grand Canyon That's Incredible, It's What's Missing

Our trip last week started in Las Vegas, Nevada, where we paid a visit to an exposure of the "Great Unconformity" which is also seen in the bottom of the Grand Canyon. A participant noted that he had seen Copperfield make an elephant disappear once, but that this week he had seen a geologist make a billion years disappear. That's what is incredible about the Grand Canyon. There are lots of interesting rocks to see, but the story they tell is that a whole lot more rocks are missing. Many times more rocks that we can see.

No part of the crust holds a complete story of the Earth. There simply hasn't been a spot that has been stable enough through the billions of years of geologic time to continually collect sediments. Instead, the story of every place one can ever visit on Earth is that it has been uplifted, eroded, deformed, and subsided numerous times. The Grand Canyon has been unusually stable compared to most, but still there are huge gaps in the story. These gaps where erosion took place are called unconformities. There are at least fourteen of them exposed in the Grand Canyon.

The most obvious kind of unconformity is called an angular unconformity and the eastern part of the canyon exposes one of the most famous examples in the world. It separates the tilted rocks of the Grand Canyon Supergroup from the flat-lying Paleozoic sediments that make up the most visible part of the canyon walls. Sediments more than 12,000 feet thick once covered the region. They accumulated between 1.25 billion and 700 million years ago, but were eventually broken and tilted by faulting. Almost all the rocks were eroded away except for isolated blocks such as those seen in the picture above.

The second kind of unconformity divides older metamorphic and igneous rocks from younger flat-lying sediments. It is called a nonconformity. It is one of the most profound in the region, as the old metamorphic rocks represent the roots of a vast mountain range many thousands of feet high that was completely eroded away to a flat plain. The gap between the rocks extends from 1.7 billion years to just 500 million years ago.

If you ever have the opportunity to raft the Colorado River, be sure to stop in Blacktail Canyon and walk a short distance up. It's gorgeous in its own right, but is one of the best places in the entire canyon where one can lay a hand across a billion years.

Photo by Mrs. Geotripper

 The third type of unconformity is a disconformity, where there are horizontal sediments both above and below the surface of erosion. Most of the boundaries between the Paleozoic formations making up the bulk of the canyon walls are disconformities. The time gap between the Cambrian layers of the Tonto Group and the Mississippian Limestone is more than 100 million years (in the picture below). For perspective, consider that 100 million years ago, dinosaurs still dominated terrestrial habitats on Earth.

The black lines are disconformities, places where erosion has removed rocks.

Most written descriptions and interpretive signs emphasize the thickness and nature of the rocks exposed in the Grand Canyon. J. Michael Timmons and Karl E. Karlstrom, in their wonderful work Grand Canyon Geology: Two Billion Years of Earth's History, have taken a different tack in representing the rocks. Their stratigraphic column showing the formations in the canyon also shows the approximate time frame of the time periods that are missing (in white).

It's not an unconformity, but the other rocks that are missing from the Grand Canyon are the roughly two miles of sediments that once lay on top of the Kaibab Formation. We know they were there because they are found all around the Grand Canyon region, but they've been removed by the unrelenting forces of erosion. All told, there are about 4,000 feet of Paleozoic rocks making up the walls of the Grand Canyon. But there are in excess of 25,000 feet of sediments that have been removed, and a similar amount of metamorphic and igneous rocks as well.

The Grand Canyon is incredible, but the missing rocks of Grand Canyon are extraordinary!

Where are the Ten Most Incredible Places You've Ever Stood? My Number 2: The Grandest Canyon of All

A clearing storm in Carbon Canyon, a tributary to the Grand Canyon

Of course, the Grand Canyon was going to appear on a list like this. It is one of the great spectacles of geology on planet Earth, and it has been entwined with my life many times over. I can trace the first inklings of my curiosity about geology to a vacation at the North Rim when I was a child of nine or ten. Picking up fossils in a meadow along the highway north of the park, I wondered how they could have ended up at 8,000 feet above sea level. A decade later I was a gawky thin teenager in his first year of college looking for direction in his life. A week below the rim on the New Hance and Grandview trails with an inspirational professor provided the impetus for following a career in geology. And then there has been the nearly three decades of leading students to this stunning place, introducing them to this most incredible gorge and the geological history it reveals. Yes, the Grand Canyon is one of the ten most incredible places I've ever stood.

The Desert View Watchtower on the eastern edge of the South Rim of Grand Canyon.

But there is a problem with picking the Grand Canyon as one of my "spots". It's a really big place! There are 200-plus river miles, the canyon is a mile deep and ten or fifteen miles wide, and has countless side canyons and tributaries (so many that a lot are named after their mileage along the river, i.e. Two-hundred Mile Canyon). Many of the side canyons would be national parks of their own in any other setting; Havasu Canyon and National Canyon are tens of miles long, and just as deep as the main gorge.

Mather Point, possibly. I didn't label this one!

So do you pick the rim? This is where most people see the canyon for the first time. There are two rims of course, the North and the South. Probably 90% of the park's visitors come to the South Rim, and that is where most of the facilities are located. It has some grand viewpoints, including, um, Grandview Point. I love visiting there, but it isn't the most incredible part I've stood on.

The North Rim is distinctly different. A thousand feet higher than the South Rim, it is covered with an extensive cool forest of fir and ponderosa. It's lonelier, with a single resort, a small camper store and a campground (check out the excellent Geogypsy Traveler blog for the perspectives of a North Rim ranger). No matter where I am on the North Rim, it feels more wild. It's one of my most cherished places in the world. But I can't pick out a single spot that I've stood on that set it apart from other areas of the canyon.

There are the archaeological sites. People have lived on and in the Grand Canyon for more than 4,000 years, and have left behind intriguing clues about their lives and beliefs, including the split-twig figurines and multitudes of petroglyphs and pictographs. Had I not ended up a geologist, I would most certainly have followed archaeology as a career. The Grand Canyon has some great archaeology, but I couldn't pick a single spot that represents all the canyon means to me.

It took a lot of consideration, but in the end, I knew the "spot" would have to be Hance Rapids at Mile 77 on the Colorado River. So many things in my life converged at this spot. The New Hance Trail reaches the river at this point. I walked the trail in 1976 on my first geology field studies trip and stood on the shore of the Colorado River for the first time. I had walked through 1.7 billion years of earth history to reach this spot, seeing the rocks I had been studying in class for the previous two months. The history of the canyon came alive to me as I walked in wonderment, seeing the crossbedding in sandstone caused by wind blowing over dunes 300 million years ago, the footprints of pre-dinosaurian reptiles and amphibians, the ripplemarks of long-gone rivers and beaches, and fossils from times before multicelled life existed on the planet.

It is at this point that river-runners first encounter the Granite Gorge, the Inner Canyon of the Grand Canyon. The rocks are schist and gneiss 1.7 billion years old  that formed in the roots of a long-gone mountain range that until recently was hidden in the deep crust of the lithosphere. Only in the last five or six million years has the Colorado River exposed these rocks to view. It was near this spot that John Wesley Powell wrote his immortal words about the Grand Canyon: "We are now ready to start on our way down the Great Unknown...We are three quarters of a mile in the depths of the earth...We have an unknown distance yet to run, an unknown river yet to explore. What falls there are, we know not; what rocks beset the channel, we know not; what walls rise over the river, we know not."

The Great Unconformity separates these ancient rocks from the only somewhat younger rocks of the Grand Canyon Supergroup (the reddish sediments on the right in the picture below).  The Supergroup is a group of late Proterozoic sediments that are three times as thick as the main sequence of Paleozoic rocks that make the upper 4,000 feet of the Grand Canyon cliffs. They were faulted, tilted, eroded, and ultimately buried by the advancing Cambrian sea of 515 million years ago. It may be the most famous unconformity on the planet.

This was the spot where I became a geologist.

I returned to Hance Rapids last summer for the first time in thirty years, only this time I came by raft rather than by foot. I am still processing that journey in my mind, but I already know that it was one of the most significant events in my life. I became aware of the fragile nature of life, first among the plants and animals in this challenging environment, but also of my own. Aside from the profound risk of driving a car every day, I came the closest I've ever been to realizing the possibility of death when I was dumped into the near freezing water and rode the toughest rapid for more than a quarter of a mile. We went over more than 150 rapids in seventeen days, and Hance was the first of the monster rapids, rated 8 or 9 on a scale of 10.

Some pictures surfaced a couple of years ago on my Facebook page of that first profound adventure that I had in 1976. It's remarkable how little the river and the rocks have changed, but I realized how much has changed in our understanding of how the rocks of the canyon accumulated, and how the canyon itself came into being. Plate tectonics had been accepted only a few years prior to my arrival in the canyon, and the tectonic history was only just then getting worked out. Parts of the story are still mysterious.

I also realize the massive changes in my own life since then. Back then, there was a dedicated geology professor discussing the history of the canyon, and a young man making life-changing decisions in the professor's class. The young man had not yet married, there were no children in his life, he had not earned a living on his own. He was just starting out.

Today, my kids are grown, I get awards for longevity at my job, and I'm closer to the end of my career than I am to its beginning. I am a teacher now, but I continue to be a student as well, seeking out new places, and revisiting the old ones from the past for continuing enlightenment. The canyon will continue to exist, changed only in a few ways during my tenure on the planet. It knows or cares little of the latest life form that scrabbles about its surface, and it will shrug off the gigantic reservoirs we've constructed to try and control the river.

The canyon is an incredible place. It gives us perspective in so many ways, and that's why it ended up as number two on the list of the most incredible places I've ever stood.

Just who is that thin person in the yellow jacket??

Into the Great Unknown: Crossing the Great Unconformity Again; But Which One?

Every day is new. Every day the Canyon is different...

I look back over the notes of my journey down into the Great Unknown, the Colorado River through the Grand Canyon, and I am struck by the number of times I mention change. By mile 80 we had passed through essentially all the major rock units of the Grand Canyon, and one can be forgiven for thinking that things might get repetitious, but it just never happened. I was now fifty miles farther downstream, and every morning, every day produced new revelations. I knew by now on Day 11 that I was having one of the most incredible experiences I would ever have in my life, and still five days remained.

The day began as a sort of "passages" kind of journey. We needed to make 15 miles or so, and there was just one excursion up a side canyon in the plan. But there were also some big rapids to worry about, including Specter, Bedrock, and Deubendorff, as well as seven smaller ones. I could tell I was still a bit spooked after my swim down Crystal Rapid a few days earlier.

Enfilade Camp was on a sandy beach below a large terrace that promised a decent view. My nephew had hiked up the previous evening and had come face to face with a bighorn ram, so I was a bit curious to see what would be around in the morning. I found a nice view upstream and downstream, and a lot of sheep tracks and droppings, but none of them were visible (of course, given their excellent camouflage, they were probably there watching me).

We started the day in the Bright Angel Shale of Cambrian age, but before long we entered into the Granite Gorge again. It's interesting how we refer to the "Granite Gorge" when so much of it is actually composed of black schist. I was just stunned by the polished surfaces that looked all the world like obsidian, even on slopes dozens of feet above the river.

 The canyon walls closed in once again, and the schist cliffs rose high above us.

In eleven days we had dropped 1,200 feet or more, and the flora was picking up a definite Mojave-Sonoran flavor. Barrel cacti were common on the slopes above the river. Within a day or so we would be seeing ocotillo.

We reached Bedrock Rapid (6-8) and stopped to scout. It was appropriately named, as a big chunk of granite and schist split the river. If a boat went to the left, it would be caught in a too-small current and impossible eddy. But the river right tried to dash the boats against the rock outcrops. It took some hard rowing, but the boatmen got us through just fine. We bounced off a boulder, but it was done quickly and we were okay.

The river at Bedrock Rapid tries to mash my brother and sister-in-law against a cliff. I give them credit for carefully observing the geology.

Below the rapid I saw one of those extraordinary sights that seem to occur with continuing regularity. I've mentioned the Great Unconformity, and we saw a wonderful exposure in Blacktail Canyon, described in the previous post. The ancient erosion surface separates 500 million year old sediments from 1.7 billion year old metamorphic rocks.  It is marvelous to be able to lay one's hands on 1.2 billion years of missing history.

But the canyon hides secrets, and one of them is that rocks exist that fill that void. There are in fact lots of rocks, in layers about 12,000 feet thick. We had visited them earlier in the trip, in the area between Nankoweap and Hance Rapid. They too rest on a "great unconformity" spanning 500 million years. They in turn are overlain by the Tapeats Sandstone. Because the Supergroup has been tilted, they contact the rocks above at an angle, so this contact is known as an angular unconformity.

Above Bedrock Rapids, both unconformities could be seen in the same outcrop! The sun was at a difficult angle, so if you can't see it, take a look at the labeled version below. I've drawn this kind of rock relationship on chalkboards many, many times, but I haven't seen as many of them in the real world.

Downstream we encountered Deubendorff Rapid (5-8). As we bulled our way through, we caught the edge of a hole and lost an oar. Pete worked with the remaining oar, but got us through okay, if not a bit soaked.

Drifting along the river below, we encountered the second extraordinary sight of the day. Dikes and sills are the result of molten material forcing its way through solid rock. Dikes cut across the previously existing rock, while sills squeeze their way between layers. You can see examples of dikes, but few sills on my Geotripper Images website, and that's the thing: I don't have many pictures of sills.
As we came around the bend of the river, a black cliff came into view, a layer that ran parallel to the enclosing layers of Bass Limestone and Hotauta Conglomerate (these form the base of the Grand Canyon Supergroup). It was a basaltic sill of huge proportions. The precise name of the rock is diabase, which was a shallow intrusion that was neither extrusive in texture (fine-grained) or intrusive (coarse-grained). It's a grain-size in-betweener.

It was one more stunning sight in a canyon with many of them.

Soon after, the river re-entered exposures of the Granite Gorge Intrusive Suite, and the canyon narrowed. A lot. The walls of schist rose straight out of the river and soared for hundreds of feet. Just past Mile 135 we traveled through the narrowest gorge in the entire Grand Canyon, the Granite Narrows. It was only 76 feet wide. The river was over 100 feet deep!

It had been an incredible day, but the best part was just ahead. More on that in the next post!