Curious Nature: The unique geology of Tenmile Canyon | VailDaily.com
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Curious Nature: The unique geology of Tenmile Canyon

Carly Innis
Curious Nature
The north end of Tenmile Canyon, near Frisco. Due to unique geological processes, the stretch of I-70 through Tenmile Canyon presents a peculiar, yet jaw-dropping landscape that is quite unique.
Courtesy photo

While driving for a geology field trip, my college professor once told the class that the most common cause of death of geologists is a car accident. This was surely a made-up statistic, but he gave the logical reasoning that while driving, geologists are always looking out the windows and wondering, “what the heck is that?!”

Within a single drive along Interstate 70, locals, visitors and geologists alike can take a look out their window and observe the curious geology of all the mysterious rocks, peaks and canyons that make up the Colorado landscape. How did dynamic processes of uplift, faulting and erosion create landscapes so different and so unique? Much more simply put: What the heck is that and how did it form?

The south end of Tenmile Canyon near Frisco, which has been shaped by glaciers, snow and water.
Courtesy photo

Exploring the beautiful mountains behind my own steering wheel has led me to fully understand my professor’s claim. Many drives I have longed for the shotgun seat and a top-down convertible to fully take in the surroundings, especially the geology.



Between Vail and Frisco, dividing the Gore Range from the Tenmile Range, is Tenmile Canyon. Due to unique geological processes, the stretch of I-70 through Tenmile Canyon presents a peculiar, yet jaw-dropping, landscape that is quite unique.

The initial uplift of the Rocky Mountains during the Laramide Orogeny created the base of the mountains in Colorado. From this mountain-building event, the Gore and Tenmile formed a continuous range. Since then, the ranges have been broken apart by faulting to form a canyon exposing the core of these mountains and the metamorphosed rock.



The TenMile Range seen from Boreas Pass. The initial uplift of the Rocky Mountains during the Laramide Orogeny created the base of the mountains in Colorado. From this mountain-building event, the Gore and Tenmile formed a continuous range.
Courtesy photo

A fault is a break in between two blocks of land or rock that can move up, down or sideways. Evidence of this type of action in Tenmile Canyon is not only in the offset of the canyon, but in the polished, lined rocks called slickensides. Visible along the east wall of the canyon, this feature formed as a result of rock sliding against rock. Some scientists believe that the canyon fault may be an extension of the Mosquito Fault, but little geologic evidence makes drawing conclusions like these difficult.

Through your car window, or sitting beside the water at Officer’s Gulch, gazing at the canyon walls, you may see metamorphosed sedimentary (metasedimentary) and metamorphosed igneous (metaignious) rocks, appearing in tight layers or smaller, packed grains. These rocks are evidence of past sediment layers and volcanic flows in the area that have undergone pressure and heat to create the transformed rock in the canyon. Shooting across some parts of the canyon walls are veins of lighter-colored pegmatite, where fractures have allowed for rock to flow and solidify.

More recently, in geologic terms, Tenmile Canyon has been shaped by glaciers, snow and water. Moraines, the build-up of rocks due to glacier movement, serve as evidence of flowing glaciers in the Tenmile region. According to local geologist Randall Streufert, the eastern end of the Tenmile glacier is established by the terminal moraine of the North-South ridge at the Frisco Peninsula.

From large landscape-shaping events to specific features such as the Tenmile Canyon, when it comes to the geologic processes that have shaped the landscape, even the best of scientists may never know the whole story. That does not mean there is not a lot to learn from the stunning geology all around. Hopefully the next time you are driving, or even better, riding as a passenger, you will take a closer look at the rocks around you and get one step closer to answering, “what the heck is that!?”


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