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.

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....

Time Beyond Imagining - A Brief History of the Colorado Plateau: Sand!

Back to our adventure through time on the Colorado Plateau. We have been mostly exploring the Proterozoic and Paleozoic history with a walk up from the bottom of the Grand Canyon where these rocks are so spectacularly exposed. There have been some side excursions to the Paradox Basin and the Ancestral Rockies, but today we reach the rim of the canyon, with a short exploration of the final three formations that make up the canyon walls (in two posts).

One of the most obvious layers in the Grand Canyon is a 300 foot high white cliff just a few hundred feet below the rim. The rock making up the cliff is the Coconino Sandstone, which formed in Permian time as sand dunes in a desert that extended across northern Arizona, New Mexico, and southern Utah (something like 200,000 square miles). The most obvious feature of the formation are the crossbeds, the sloping layers that represent the slip faces of the dunes that have been preserved in the cliffs. It is a beautiful rock formation!

When I was a new student taking my first or second class in geology, I had the opportunity to visit the Raymond Alf Paleontology Museum at Webb School in Claremont, California. I was intrigued by their spectacular collection of fossil trackways, and was curious where such ichnofossils were found. One of the sources was the Coconino Sandstone, which I would see up close only a few weeks later on my first geology field trip. There is nothing quite like finding a fossil trackway like the one illustrated above. Unlike fossil shells and bones, representing death, a trackway preserves a moment in the life of a creature. Was it running or walking, feeding or escaping? What kind of creature was it anyway? The Coconino preserves more than two dozen kinds of tracks, from large amphibians or reptiles to scorpions or spiders.

The Coconino is correlated with the De Chelly Sandstone, which forms the spectacular cliffs of De Chelly National Monument, and the wonderful John Wayne movie towers and spires of Monument Valley. Because the sand is porous, it is an important groundwater reservoir for towns to the south of Grand Canyon like Flagstaff and Williams.