Q&A: Research Geologist’s Findings Help Explain How Grand Canyon, Colorado River Were Formed

Photo courtesy of Kyle House

Photo courtesy of Kyle House

Rivers have long been a source of fascination for Kyle House, a research geologist with the U.S. Geological Survey. House’s research focuses on the Lower Colorado River, and his paper on the river’s formation and how it helped shape the Grand Canyon recently won the prestigious Kirk Bryan Award for Research Excellence from the Geological Society of America. (For a complete look at House’s project, click here.)

House’s findings have helped revitalize interest in developing a more complete understanding of the Lower Colorado River’s geologic history. We asked House a few questions about his background, his research and what’s next:

How did you get into geology, and how did you come to work for the USGS and at the Grand Canyon?
I became a geologist upon leaving the flat plains of Enid, Oklahoma, after high school to attend college in Bellingham, Washington. I attended graduate school at the University of Arizona, where I studied the history of various rivers in Arizona over a range of scales in space and time. This experience earned me an M.S. and a Ph.D. in geosciences, but it also engendered awareness that rivers are fascinating. They are systems that can create, destroy and regenerate landscapes, and their records of doing these things are decipherable when viewed through the prism of geology. I mapped several desert river and lake systems at my previous job, at the Nevada Bureau of Mines and Geology. I was on a mapping project when I stumbled upon key evidence for the origin of the Colorado River and became entranced by the problem. I spent several years working on it while at NBMG, and then, a position focused on the river opened up at the USGS in Flagstaff. Thus, I was faced with a chance to move to a favorite place and continue to study a favorite river. Obviously, I took it!

What was your goal when you began researching the geologic history of the Canyon and Lower Colorado River?
Initially, my goal was to map some well-exposed sections of what I thought was a well-established stratigraphic record. Once I learned that it was practically untapped or only well-known in select but disparate areas, I realized that there was a scientific mother lode at my feet. The fact that it spoke to the history of the Grand Canyon was a fortunate side effect. Lots of geologists study the Grand Canyon; only a few of us prefer to venture deep into the desert to study where all the mud, sand and gravel went, and how and when it got there.

The evidence you uncovered supports the theory that the Lower Colorado River has held its present course for between 5 million and 6 million years. What does this tell us about the river, and about its role in carving the Grand Canyon?
My study area lies from the mouth of the Canyon to the river’s delta in the Gulf of California. This is the reach of the river through which essentially every drop of water and every grain of silt, sand and gravel that exits the Grand Canyon must pass. The vast majority of those grains make it all the way through to the delta and the sea beyond, but some get stored in the series of short canyons and relatively long, broad valleys that characterize the valley of the Lower Colorado. There, the physical stratigraphic evidence for the evolution of the Lower Colorado River and Grand Canyon can be seen.

What we have known for some time is that beginning immediately below the mouth of Grand Canyon, there is a suite of physical evidence clearly indicating that no through-going Colorado River passed through this critical area prior to about 6 million years ago. Thus, we can assert with fair confidence that prior to this time, the size, shape, and continuity of Grand Canyon was considerably different than it is now.

Our new findings were discovered in a geologic mapping project in the area of Laughlin, Nevada, and Bullhead City, Arizona. It was a joint project between the Arizona Geological Survey and the Nevada Bureau of Mines and Geology that was funded primarily by the USGS. Our “golden section” was found adjacent to a casino (Harrah’s) in Laughlin. There, in a short, steep and sun-baked ravine, we found a stack of geologic deposits containing a clear record of this sequence of events: no river present in the valley; occurrence of large flood from upstream; formation of a lake; drainage of lake; thick sedimentation associated with a permanently through-going, large river.

This finding offered tremendous support to an idea of river integration via spilling lakes. We eventually determined that there was no river present downstream from Hoover Dam before about 5.5 million years ago, but within less than 1 million years, the river had arrived in full force and filled the valleys with hundreds of feet of sediment.

Did your findings surprise you?
The discovery of the “golden section” next to the casino came as a huge surprise. You never know what you may find when mapping the desert. Our findings contrasted sharply with conventional wisdom about how this part of the system evolved. The predominant line of thinking involved a complex series of steps involving inundation by the sea; erosion of an early river; drainage capture near the central Grand Canyon area; retreat of the sea; advance of the river; and uplift of the general region of the lower river.

In contrast, the “spilling lake” model requires no advance and retreat of the sea, no headward (upstream directed) erosion through steep mountains, and no regional uplift. Thus, it is a far simpler explanation for the stratigraphic record and the modern landscape.

What’s the next step in this area of research?
The Lower Colorado River Valley is a critical national resource for water supply to some of the largest cities in the Western U.S. It is also a key recreational resource. We need to have a clear understanding of the geologic and hydrologic history of this important area. Our recent work has highlighted this area as one containing a spectacular geologic record. This, in addition to its value as a resource to the American people, has led to the development of a USGS geologic mapping project focused on the valley and its geologic history. Last year, we began a project to map the entirety of the lower river, from Hoover Dam to Yuma. It will be the first such project to focus on this reach as a whole.

Anything else you’d like to mention?
The Lower Colorado River is a true natural wonder: a large river that heads in the Rocky Mountains and ultimately courses through one of the Earth’s hottest deserts. Of course, it is highly regulated now, but to see it during its heyday — as it carried large pulses of snowmelt runoff through the sweltering, foreboding desert landscape of its lower valley — would have been a deeply awe-inspiring experience. Creating geologic maps that document the evolution of this interesting natural system is the closest that we can come to understanding its history, its grandeur and possibly its future.

 

—Noah Austin

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