Wind River Canyon

On Friday we left Nebraska and continued to Wyoming. Following US 20 took us through Wind River Canyon, with spectacular views of rocks representing almost 3 billion years of the Earth’s history.

Traveling on US 20 westbound, you approach the canyon from the south, driving over Eocene sedimentary rocks. Just before entering the canyon you cross the Owl Creek Mountains Thrust Fault. Rocks north of this fault (everything in the canyon) have been pushed up over the Eocene. This brings you suddenly into much older rocks, like the red-colored Chugwater Formation rocks from the Triassic Period, shown above.

Continuing north, you cross the Boyson Normal Fault. The fault itself is not visible in the photo below, but the layered rocks on the left (which are Mesozoic in age) lie south of the fault, while the more amorphous rocks on the right lie to the north. There is also a small reverse fault visible in the Mesozoic rocks.

Crossing the Boson Fault brings you into much older rocks; 2.9 billion-year-old (Archean Eon) metamorphic rocks, the oldest rocks in Wyoming:

Next up are huge thicknesses of Cambrian, Ordovician, and Mississippian sandstones, limestones, and dolomites. These rocks are generally strong and resistant to weathering, and form steep canyon walls up to several thousand feet high:

Continuing north, you pass by Pennsylvanian and Permian sandstones with large crossbed sets, which represent sand dunes:

Finally, as you exit the canyon and approach the town of Thermopolis, you pass back into the same Triassic formations that were present at the south end of the canyon:

The Geologic Society of America has a Wind River Canyon Field Guide, by Edwin Maughan, which is available for download (pdf format).

Thermopolis is only a few hours south of our destination, and by late Friday afternoon we arrived at Shell Campground.

Saturday was spent taking care of logistics and additional arrivals. Tomorrow, if the weather holds (thunderstorms are forecast), we head out to the site.

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