Monday, January 4, 2016

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.
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