Most park visitors first see the Teton peaks from the highway. Whether
they drive in from the south, east, or north, there is one point on the
route at which a spectacular panorama of the Tetons and Jackson Hole
suddenly appears. Part of the thrill of these three views is that they
are so unexpected and so different. The geologic history is responsible
for these differences.
_View north._—
Throughout the first 4 miles north of the town of Jackson, the view of
the Tetons from U. S. 26-89 is blocked by East Gros Ventre Butte. At the
north end of the butte, the highway climbs onto a flat upland at the
south boundary of Grand Teton National Park. Without any advance
warning, the motorist sees the whole east front of the Teton Range
rising steeply from the amazingly flat floor of Jackson Hole.
From the park boundary turnout no lakes or rivers are visible to the
north but the nearest line of trees in the direction of the highest
Teton peaks marks the approximate position of the Gros Ventre River. The
elevation of this river is surprising, for the route has just come up a
150-foot hill, out of the flat valley of a much smaller stream, yet here
at eye-level is a major river perched on an upland plain. The reason for
these strange relations is that the hill is a fault scarp (see fig. 16A
for a diagram) and the valley in which the town of Jackson is located
was dropped 150 feet or more in the last 15,000 years.
On the skyline directly west of the turnout are horizontal and inclined
layers of rocks. These once extended over the tops of the highest peaks
but were worn away from some parts as the mountains rose. All along the
range, trees grow only up to _treeline_ (also called _timberline_—a
general elevation above which trees do not grow) which here is about
10,500 feet above the sea. To the southeast and east, beyond the
sage-covered floor of Jackson Hole, are rolling partly forested slopes
marking the west end of the Gros Ventre Mountains. They do not look at
all like the Tetons because they were formed in a very different manner.
The Gros Ventres are folded mountains that have foothills; the Tetons
are faulted mountains that do not.