Travel Reference
In-Depth Information
The wide Snake River flows past the Tetons.
The Tetons and How They Got So High
The name Tetons (Les Trois Tetons—The Three Teats in the somewhat indecent French of
the early trappers) comes from the three great summits you can see from the Idaho side,
although there are many more than three peaks in the range. These mountains are truly
awe inspiring: 12 peaks exceed 12,000 feet (3,650 m), and the Grand Teton is 13,770 feet
(4,197 m) high.
The striking difference in elevation from that of Jackson Hole is what makes these
mountains so special. There aren't a lot of places where you can gaze up at a sky full of
mountain peaks whose tops are 5,000 to 7,500 feet (1,500-2,300 m) above you while you
stand at their base—with no foothills in between! As author Owen Wister wrote over one
hundred years ago: “The way in which they come up without any heralding of foothills
seems as though they rose from the sea.”
How did these mountains get so high? The eminent author John McPhee, although not
a geologist, describes the process in his book,
Rising from the Plains:
“he crust extends,
the earth stretches, the land pulls apart—and one result is a north-south-trending normal
fault, fifty miles long. On the two sides of this fault, blocks of country swing [as though]
on distant hinges like a facing pair of trapdoors—one rising, one sagging. The rising side is
the rock of the nascent Tetons, carrying upward on its back the stratified deposits.”
Geoscientists have proven that the Tetons certainly
did
rise, though not from the sea,
as it seemed to Wister. This range of mountains was formed as part of the east-west pulling
apart of the North American plate—an activity that is still going on from Arizona to Idaho
and Wyoming. In the Teton area, when the pulling apart overcame the strength of the
rocks, they broke to form
a fault
where the two sides move past each other. This fault runs
roughly north to south and slants down steeply to the east. The more the rocks are pulled
apart, the more space needs to be filled in. The block that is sinking helps to fill the gap
that would otherwise develop.
The steepness of the mountain front that looms over Jackson Hole testifies to the
strength and resistance to erosion of the 2.7-billion-year-old rocks recently exposed by the
fault. The fault is still active, the land continues to sink, and the mountains continue to rise,
but streams have brought sediments in to fill the valley floor. This process has been going
on for about 7.5 million years so far, according to
Creation of the Teton Landscape
by David
D. Love, John C. Reed, and Kenneth L. Pierce (Grand Teton Natural History Association,
2003).
