The Tetons are a short, narrow, and high mountain range, distinctive in
the midst of the great chain of the Rocky Mountains, the backbone of
western North America. Figure 1 shows how the Tetons and their
surroundings might appear if you viewed them from a satellite at an
altitude of perhaps a hundred miles. The U. S. Geological Survey
topographic map of Grand Teton National Park shows the names of many
features not indicated on figure 1 or on the geologic map inside the
back cover. The Teton Range is a rectangular mountain block about 40
miles long and 10-15 miles wide. It is flanked on the east and west by
flat-floored valleys. Jackson Hole is the eastern one and Teton Basin
(called Pierre’s Hole by the early trappers) is the western.
The Teton Range is not symmetrical. The highest peaks lie near the
eastern edge of the mountain block, rather than along its center, as is
true in conventional mountains, and the western slopes are broad and
gentle in contrast to the precipitous eastern slopes. The northern end
of the range disappears under enormous lava flows that form the
Yellowstone Volcanic Plateau. Even from this altitude the outlines of
some of these flows can be seen.
On the south the Teton Range abuts almost at right angles against a
northwest-trending area of lower and less rugged mountains (the Snake
River, Wyoming, and Hoback Ranges). These mountains appear altogether
different from the Tetons. They consist of a series of long parallel
ridges cut or separated by valleys and canyons. This pattern is
characteristic of mountains composed of crumpled, steeply tilted rock
layers—erosion wears away the softer layers, leaving the harder ones
standing as ridges.
On the east and northeast, Jackson Hole is bounded by the Gros Ventre
and Washakie Ranges, which are composed chiefly of folded hard and soft
sedimentary rocks. In contrast, between these mountains and the deepest
part of Jackson Hole to the west, thick layers of soft nearly flat-lying
sedimentary rocks have been sculptured by streams and ice into randomly
oriented knife-edge ridges and rolling hills separated by broad valleys.
The hills east of the park are called the Mount Leidy Highlands and
those northeast are the Pinyon Peak Highlands.