Highway 26 in eastern Idaho passes through soaring plateau country where I felt like I could reach out and touch the mountains peaks. At Swan Valley I crossed the sinuous Snake River once again before turning onto highway 31, and then climbed steeply to Pine Creek Pass at an elevation of 6764 ft above sea level.
Highway31 PineCreekPass EasternID
Soon the road dropped down into Teton Valley and Victor, ID. Like shingles overlapping one another on a westward-sloping roof, the mountains to the east of Victor look to be the result of compression and contraction of Earth’s crust during the Sevier orogeny, a period of mountain building that occurred from roughly 150 to 55 million years ago. This overthrust belt is a segment of an immensely twisting trend of folds and thrust faults extending along the western edge of the continent from Alaska to Mexico.
(b)Highway31Near VictorID
Grand Teton is visible in the distance on the left, a distinctive ragged, jagged peak jutting skyward on the eastern side of the thrust-faulted mountains. Separating the high mountains and valleys of western Wyoming from the lowland volcanics of the Snake River Plain, the Tetons present themselves as a breath-taking wall of rock.
My overloaded mini-tank of a Subaru wheezed up Teton Pass (elevation 8431 ft) in third gear, passing a utilities truck like it was standing still. Oh, wait – the truck was standing still. At the Pass, Jackson Hole came into view.
Hwy22Into JacksonHoleWY
The east flank of the Tetons is much different than the west. Unlike the compressional or thrust faults present on the west side of the range, the east flank is bounded by a gigantic normal fault which has raised the Teton Range and dropped Jackson Hole. As mentioned in a recent post, the Teton fault is the easternmost normal fault separating the Great Basin and Rocky Mountains. Additionally, the crustal extension and thinning caused by normal faulting occurred millions of years later than the thrust faulting seen on the west side of the range. The Tetons are a result of geologic processes pulling apart the crust in an east-west direction. These processes continue today.
BreakInSlopeTetonRange
A break in slope occurs where the steep mountains meet the valley floor, and this occurs with dramatic elegance at the eastern base of the Teton Range. Here we witness the trace of the Teton Fault. The fault can be seen along the highway north from Jackson, easily identified by the steep slopes or fault scarps showing up as darker areas at the base of the mountains.
And so I continued north towards Yellowstone…
