Creation of the Teton Landscape: The Geologic Story of Grand Teton National ParkReed, John C. (John Calvin)
Science
Creation of the Teton Landscape: The Geologic Story of Grand Teton National Park
Reed, John C. (John Calvin)
Geology -- Wyoming -- Grand Teton National Park
The view east presents the greatest contrasts in the shortest
distances—the flat floor of Jackson Hole is 3 miles away and 7,000 feet
below the top of the Grand Teton. Along the junction of the mountains
and valley floor are blue glacial lakes strung out like irregular beads
in a necklace. They are conspicuously rimmed by black-appearing margins
of pine trees that grow only on the surrounding glacial moraines. Beyond
these are the broad treeless boulder-strewn plains of Jackson Hole.
Fifty miles to the east and northeast, on the horizon beyond the rolling
hills of the Pinyon Peak Highlands, are the horizontally layered
volcanic rocks of the Absaroka Range. Southeast is the colorful red,
purple, green, and gray Gros Ventre River Valley, with the fresh giant
scar of the Lower Gros Ventre Slide near its mouth. Bounding the south
side of this valley are the peaks of the Gros Ventre Mountains, whose
tilted slabby gray cliff-forming layers resemble (and are the same as)
those on the west flank of the Teton Range. Seventy miles away, in the
southeast distance, beyond the Gros Ventre Mountains are the shining
snowcapped peaks of the Wind River Range, the highest peak of which
(Gannett Peak) is about 20 feet higher than the Grand Teton.
Conspicuous on the eastern and southeastern skyline are high-level
(11,000-12,000 feet) flat-topped surfaces on both the Wind River and
Absaroka Ranges. These are remnants that mark the upper limit of
sedimentary fill of the basins adjacent to the mountains. A plain once
connected these surfaces and extended westward at least as far as the
conspicuous flat on the mountain south of Lower Gros Ventre Slide. It is
difficult to imagine the amount of rock that has been washed away from
between these remnants in comparatively recent geologic time, during and
after the rise of the Teton Range.
From this vantage point the mountaineer also gets a concept of the
magnitude of the first and largest glaciers that scoured the landscape.
Ice flowed southwestward in an essentially unbroken stream from the
Beartooth Mountains, 100 miles away, westward from the Absaroka Range,
and northwestward from the Wind River Range (fig. 57). Ice lapped up to
treeline on the Teton Range and extended across Jackson Hole nearly to
the top of the Lower Gros Ventre Slide. The Pinyon Peak and Mount Leidy
Highlands were almost buried. All these glaciers came together in
Jackson Hole and flowed south within the ever-narrowing Snake River
Valley.
The view south presents a great variety of contrasts. Conspicuous, as in
the view north, is the asymmetry of the range. South of the high peaks
of crystalline rocks, gray layered cliffs of limestone extend in places
all the way to the steep east face of the Teton Range where they are
abruptly cut off by the great Teton fault.
Public-domain text, read in full here on John Shaqi.
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