Dreams of Summer: If there's a Little Colorado River, is there a Little Grand Canyon?

In the last post, I noted that there is a lot more to the Colorado Plateau than the Grand Canyon. The Canyon (it just has to be capitalized) is more than 200 miles long, but it cuts through just a part of the Colorado Plateau Province, a vast region encompassing 130,000 square miles (337,000 sq km), and containing 27 national parks and monuments. The Grand Canyon is a starting point, a jumping-off place so to speak, for learning the complex geological story of the American West. Our field studies course would eventually include five states beyond California.

As we left Grand Canyon National Park, we followed Highway 64 east onto Navajo Reservation lands near Cameron. The geographic region is known as the Navajo Section, and is generally lower than the high plateau that contains the Grand Canyon. For the most part the section contains flat barren badlands, although parts are very colorful (this area is sometimes called the Painted Desert). There is an exception to the flatness, where the Little Colorado River approaches the Grand Canyon. That was our next stop.

The Little Colorado River is by watershed area one of the most important tributaries of the Colorado River, but the area it drains is so arid that the river contributes little overall to the discharge of the main river. The smaller river is actually dry along most sections for most of the year. The exceptions are during the spring runoff, and during the summer monsoons. Flash floods on the small river can be monstrous. Our local river back home, the Tuolumne, is considered a fair-sized river (by California standards). It reaches flood stage at a discharge of 9,000 cubic feet per second (cfs). The highest flow ever recorded on the Tuolumne was around 70,000 cfs. During a flood in 1923, the Little Colorado River recorded 120,000 cubic feet per second!

So, as I asked in the title, if there is a Little Colorado River, is there a little Grand Canyon? In a manner of speaking, the answer is certainly yes. The lower part of the Little Colorado where it approaches the main river is a stupendous gorge 3,000 feet deep. If the Grand Canyon didn't exist, the canyon of the Little Colorado River would probably be a national park all its own. That said, the gorge of the Little Colorado River wouldn't exist without the Grand Canyon nearby. It was the rapid downcutting of the Grand Canyon that caused the gradient of the Little Colorado River to increase and carve downwards. The nature of the river canyon tells us it once flowed over a relatively flat floodplain. The evidence lies in the presence of entrenched river meanders.

Goosenecks of the San Juan River in southern Utah

Meanders are the characteristic loops and bends of a river flowing over a relatively flat surface. They are very common on rivers like the Mississippi. If the land rises, the river speeds up and starts to erode the channel downward while maintaining the shape of the meander. Eventually the river erodes a deep canyon that has intricate loops. The lower reaches of the Little Colorado has a lot of them. The San Juan River in southern Utah has also done the same thing, and a spot called the Goosenecks provides a bird's-eye view. I've included a shot of the Goosenecks above.

A distant view of the canyon of the Little Colorado River from Highway 64

If the Grand Canyon is awesome by virtual of distance and open space (a yawning chasm a mile deep and 10-15 miles wide), the canyon of the Little Colorado River is awesome by intimacy, in an odd way. The canyon where we visited had vertical walls a thousand feet (~300 meters) high, but was almost narrow enough to fling a pebble across (it least it looks that way). When you stand at certain points, you are looking straight down on the the river, as can be seen in the picture below. There aren't a lot of places where one can do this sort of thing.
It had been years since I had seen water flowing in the Little Colorado River, but last summer was remarkable in terms of the monsoons. They began early and produced a number of flash floods throughout the region. When we arrived, the river was flowing, although the term "river" barely applied to the viscous mixture of mud and silt in the canyon below.

Mouth of the Little Colorado River in Grand Canyon

The mud certainly influences the Colorado River. The Little Colorado River may not provide prodigious amounts of water to the system, but it is one of only two major sources of sediment to the river now that Glen Canyon Dam prevents mud from flowing downstream of the reservoir. When we rafted to the mouth of the Little Colorado in 2013, the main river was almost clear, but silt was pouring from the tributary. For a short distance, the river was bi-colored, but within a mile or so the water and silt were thoroughly mixed and remained that way for the remainder of our trip, another nine days!

Two rivers in one, the green Colorado, and the brown Little Colorado

The Little Colorado River is a fascinating part of the plateau country. It gets lost in the broader scenery at times, but is well worth the bit of effort to explore a few of its secrets.

Into the Great Unknown: Passing Through the Permian Period

When we pushed the rafts off the beach at Lee's Ferry, my normal sense of time disappeared. For my journey into the Great Unknown, I didn't have a watch, and my smartphone was safely ensconced in one of the vehicles. My laptop never made it beyond Phoenix. Time took on a new meaning.

There was river time. That one is controlled by the sun, mostly. There was twilight and dawn, which guided when one went to bed, or arose. There was star time, the sweep of the Milky Way that told you the stage of the nighttime you had awakened in. There was worst sun time, the baking hot part of the day that often guided the choice of lunch spots. And there was afternoon shadows time, that told us it was time to pick a campsite. 

Then there was geology time. As we descended through the first 80 miles of our river journey, we weren't just following the flow of the river downhill, but were also making our way back in geologic time. As the canyon deepened (or as the cliffs rose higher around us), we were encountering a sequence of successively older and older rocks. The youngest rocks, about 250 million years old, were exposed at Lee's Ferry, and at Mile 80 we would encounter some of the oldest rocks in the canyon, at 1.7-1.8 billion years.

As we started down the river, there were still small waterfalls tumbling off the cliffs, courtesy of the just-ended cloudburst. I was especially entranced by the double fall at Mile 4, which was trickling over ledges of the Kaibab and Toroweap formations. The Kaibab, which is familiar to all visitors at Grand Canyon National Park, forms the rim of the Grand Canyon. It is a sandy limestone that formed in a tropical shallow marine environment that developed at a time when the supercontinent Pangea had come together. The Toroweap Formation is broadly similar to the Kaibab, but is a limey sandstone. The difference might not mean much to non-geologists, but it means much to geologists who are interpreting the environment in which the rock formed. Where the Kaibab formed in offshore shoals and reefs, the Toroweap formed along the sandy coastline. Both formations are highly variable and the Kaibab especially has a rich fossil record, including corals, bryozoans, sponges, clams, gastropods (snails), and the occasional shark tooth.

Within a few million years, 90% or more of the species found as fossils in these rocks (and all other rocks worldwide) would be gone in the greatest extinction event of all geologic history. This event did not involve the dinosaurs; instead, it quite possibly made it possible for the dinosaurs to evolve and rise to dominance in terrestrial environments.

We would see the Kaibab and Toroweap formations at river level for less than 4 miles. They would be visible at times during the rest of the trip, but only as remote cliffs as much as a mile above us. At Mile 4, under another trickling waterfall (below), we crossed the contact between the Toroweap Formation, and dropped into exposures of the Coconino Sandstone. We passed beneath the Navajo Bridges at Mile 4.5, and I knew suddenly that we were indeed beyond all parts of the Colorado River with which I had any familiarity.

The Coconino Sandstone is an extraordinary rock unit. It has a distinctive pattern of crossbedding, a sort of diagonal layer formed as sand cascaded down the slipface of a sand dune. The crossbedding can be seen above just over the river vegetation. It formed in early Permian time as sand dune “sea” in a desert that extended across northern Arizona, New Mexico and southern Utah and extending north as far as present-day Montana. The Coconino preserves more than two dozen kinds of tracks, from large amphibians or reptiles to scorpions or spiders. We didn't see any of them because the Coconino was exposed along the river for only about a mile, and we weren't ready to stop yet.

By Mile 5, we had reached the contact of the Coconino with the underlying Hermit Formation (or Hermit Shale as I learned it). The Hermit is a bright red-brown formation composed primarily of silt and shale that formed in the coastal floodplains of an extensive river system. The rivers were coming from somewhere geologically special, but I'll have to save that for our next post. The Hermit was just the tail end of an important geological event in the region during late Paleozoic time.

People can be forgiven for thinking that the Colorado River carved the Grand Canyon. That's true in one sense, but a river can generally only cut downwards, and it cannot account of the vast breadth of the tributaries and side canyons. Once a steep gorge has been carved, instabilities are introduced (i.e. oversteepening of slopes) that leads to mass wasting, in other words, landsliding. Much of the canyon has been produced by a combination of landslides and debris flows/flash floods. We passed numerous examples in the first days of the trip, including the spectacular rockfall consisting of Kaibab, Toroweap and Coconino rocks in the picture below (to the right).

The storm damage was catching up to us as well. Not a tree was visible from Lee's Ferry or on the surrounding cliffs, but as the day progressed, the river became nearly choked with branches, cones and seeds from juniper, pinyon and other trees that grew at the upper end of the Paria River and other tributaries. We didn't have to bail the self-bailing rafts, but I often had to grab handfuls of debris from the boat after getting splashed in a few rapids.

A bit further down the river we saw another recent rockfall...

And at the ten mile mark, we passed the imaginatively named Tenmile Rock, a huge slab of Coconino Sandstone that broke away from the cliff, tumbled down the slope, and landed in the river without quite falling over flat.

It was huge!

The rapids the first day were an introduction to a pattern that would continue throughout the trip. The river flowed placidly through the canyon until we reached a tributary drainage. Debris flows emanating from these side canyons burst into the main channel, partly damming the channel, and pushing the main flow of the Colorado River to one side or another. With the constriction, the river would speed up, and smooth undulations would develop in the top of the rapid, forming a "vee" pointing downstream. The vee was bounded by lateral waves, and at some point the rower would either punch through the laterals (especially in the biggest rapids), or follow through the roller coaster of big waves in the center of the channel.

A series of eddies would form at the base of the rapid (literally a large whirlpool flowing partly upstream), allowing the first boats down a chance to take position in anticipation of assisting anyone ejected from a boat in the midst of the rapid.

The seriously big rapids had special problems, including pour-overs, holes, and exposed boulders that needed to be avoided at all costs. When approaching such rapids, the rowers would pull out, and climb to a vantage point that offered a chance to scout the rapid. A discussion of the best possible run would ensue, and the bigger the rapid, the longer the discussion (and for the rookies, increasing apprehension). An order was picked for the boats and off we would go.

Our first day included two riffles, Paria and Brown, rated 1 or 2 out of 10 on the Colorado Rapids classification system. We also were baptized by two class 5 rapids, Badger and Soap Creek. One thing became abundantly clear: don't take a Colorado River rafting trip if you hate getting wet. Literally every rapid would find a way to douse the passengers in the front of the raft. Mind you, when the temperatures were high, it was a welcome relief, and I generally looked forward to getting soaked! Even the smallest rapids could surprise; we found out later on that a boat flipped in the Paria Riffles a day or two after we came through.

You will also notice that I have few pictures of the rapids. My camera and silty, muddy water don't mix well, so when I heard the roar of a rapid coming up, I would snap a shot or two of rafts going over the edge, and when we got safely to the bottom I would pull the camera out and try to snap a shot or two looking back upstream, such as in the picture above at Soap Creek Rapid.

Our first day, we managed (after the late start) a modest 12.4 miles. We stayed that night at 12.4 Mile Camp (where do they come up with these creative names?). It was a cool evening because of the cloud cover. We knew hotter days would come, so we enjoyed the moderate temperatures. I set up camp, and after a dinner of fresh shrimp and linguini, I hit the sack.

Coming up next: the Roaring Twenties!

My First Fossil

Andrew Alden over at About.com Geology asks an interesting question: What was your first fossil? It took only a split second to take me back forty years to the North Rim of the Grand Canyon, where a 10 year old boy was on his first trip to the beautiful national park. But I had found out something strange at the small visitor center there. The ground I was walking on at more than 8,000 feet had once been on the bottom of the sea! Say what? How could that be? I was already at an age where I had figured out that Noah's Flood couldn't account for this. Where was all the water that it could even cover Mt. Everest and all the other mountains of the world? It was clear that something had happened, but I wasn't quite in a place where I could understand the idea of vast uplift across an entire region. I spent days musing about this, enough that the memory is clear after all these years.

After a few days camping and hiking around the rim (it would be quite some time before I would actually walk into the canyon, an event that caused me to become a geology major) we set out to see more sights in the region, but as we left the park, we drove through the long stretch of highway to Jacob Lake that passed through a beautiful forest and meadowland. We stopped for a few minutes and wandered into the meadow, and looking down I saw some little miniature poker chips, and realized that these were some of the ocean floor fossils I had seen pictures of in the visitor center! They were pieces of the stems of a crinoid, or sea lily, and after a few moments of searching, I had found a fossil sponge as well.

It was a seminal moment that I can count as leading directly to my choice to pursue geology as a career, and one of the great moments of my childhood. I really have to thank my folks for taking me on so many wonderful excursions when I was growing up. Life was such an adventure during my father's ever-so-brief two week vacation.

The pictures above: a view from the North Rim of the Grand Canyon, the less crowded, more verdant part of the canyon, a view of one of the numerous karst meadows north of the rim, and a sampling of some brachiopods, crinoids and sponges found in the Permian Kaibab Formation.

Time Beyond Imagining - A Brief History of the Colorado Plateau: A Final Transgression

With today's post we reach the rim of the Grand Canyon, and the end of the Paleozoic rocks of the Colorado Plateau. But these pictures are not of the Grand Canyon, although some similarities exist. Both canyons were carved by the Colorado River, for instance. We are in southeastern Utah at Canyonlands National Park. Our vantage point is the Island in the Sky plateau that overlooks the confluence of the Green and Colorado Rivers. Unlike the Grand Canyon, the oldest rocks visible are Permian in age, and the upper canyon walls are in Mesozoic rocks (the age of the dinosaurs, basically).

Hikers in the Grand Canyon who have a geological background don't measure their progress in miles and feet the way normal people do. We note our location by the strata through which we are strolling. The base of the Supai Group means a long slog through red dirt. The base of the Redwall almost always means a tough climb is ahead. The greatest relief to geological hikers is to arrive at the top of the Coconino Sandstone, where we realize that only two more formations lie between us and a cold beer or iced tea: the Toroweap Formation and the Kaibab Formation. Both are easily visible in yesterday's post, the Toroweap as the forested slope above the sheer Coconino cliff, and the Kaibab as the ledgy cream-colored cliff forming the rim of the canyon. Like the Coconino, both formations are Permian in age, the very latest part of the Paleozoic Era.

The Toroweap Formation is rather variable in composition, ranging from dune sands, evaporites (forming in drying bodies of water), and limestone. It formed in a time of changing sea level, where the shoreline transgressed and regressed repeatedly, forming dune fields, tidal flats and sabkhas (coastal salt flats). Fossils are generally rare, given the harsh conditions in which the rocks formed.

The Kaibab Formation is more marine in origin, being composed of limestone, dolomite, and sand. In many places chert nodules can be found. The chert is a form of altered quartz that can develop long after deposition. The layer is rich with fossils: crinoids, brachiopods, sponges, bryozoans, shark teeth, nautiloids, fish, and some of the last trilobites to inhabit the earth (the Kaibab Formation on the North Rim of the Grand Canyon was the site of my first childhood fossil discoveries). Many of these species were doomed: the end of the Permian was marked by the worst mass extinction event ever recorded. Something like 95% of all the species on the planet disappeared, for reasons that have not yet been determined, although many hypotheses are proposed.

So why the pictures of Canyonlands National Park? Note the white rock layer sandwiched between thick layers of red rock. This layer is appropriately called the White Rim Sandstone (the White Rim is a very prominent terrace in Canyonlands), and being Permian in age, is related to the Coconino, Toroweap and Kaibab formations. The sea that formed the Kaibab and other late Permian marine layers transgressed from the west onto the continent. This is indicated in part by greater thicknesses to the west. On the other hand, the farther east and north that one travels, these layers become thinner. And thinner. By the time we reach Canyonlands National Park, the marine sands are only a few feet thick and then pinch out. We are looking in these photographs at the last beach of the last Paleozoic sea.

We have reached the rim of the Grand Canyon, and the end of the Paleozoic story. The reconstruction of the supercontinent Pangea was complete. World ecosystems had been devastated by extinctions almost beyond imagining. The world had changed completely, and the Mesozoic age had begun. Dramatic changes are coming! In another post, though....