The Spires of Grand Teton National Park
Your first sight of the towering spires of the Cathedral Group -- the trois tetons (three breasts), as lonesome French trappers called them -- will create an indelible impression. A bit of history makes them even more interesting.
Their formation began more than 2.5 billion years ago when sand and volcanic debris settled in an ancient ocean that covered this entire area. Scientists estimate that roughly 40 million to 80 million years ago, a compression of the Earth's surface caused an uplift of the entire Rocky Mountains from Mexico to Canada. This was just the first step in an ongoing series of events that included several periods during which a miles-thick crust of ice covered the area. Then, 6 million to 9 million years ago, the shifting of the Earth's tectonic plates caused movement along the north-south Teton fault that produced a tremendous uplift. The valley floor also dropped precipitously. These simultaneous forces pushed the rock that is now the Teton Range to its present site, from a position 20,000 to 30,000 feet below what is today the floor of Jackson Hole. The west block of rock tipped upward to create the Teton Range, and the eastern block swung downward to form the valley that is now called Jackson Hole -- kind of like a pair of horizontal swinging doors that moved the Earth 5 miles.
After this upheaval, and after eons of erosion and glacier activity, Grand Teton, the centerpiece of this 40-mile-long fault area, towered 13,770 feet above sea level -- more than a mile above the visitor center at Moose Junction. There are eleven other peaks over 12,000 feet high in the park today, with conditions that support mountain glaciers. As you gaze upward at this magnificent range, you will notice that many of the cliffs are more than half a mile in height.
During geologic explorations of Mount Moran (elevation 12,605 ft.), which gets less attention than it deserves, it was discovered that erosion had removed some 3,000 feet of material from its summit, meaning that it once must have been more than 15,000 feet high. Equally remarkable is the fact that the thin layer of Flathead sandstone on top of this peak is also found buried at least 24,000 feet below the valley's surface -- further evidence of the skyward thrust of the mountains.
Although this is the youngest range in the Rockies -- yet another geologic anomaly -- the rocks here are some of the oldest in North America, consisting of granitic gneisses and schists, which are the hardest and least-porous rocks known to geologists.
The Teton area experienced a cooling trend about 150,000 years ago, during which glaciers more than 2,000 feet thick flowed from higher elevations, and an ice sheet covered Jackson Hole. When it melted for the final time, some 60,000 to 80,000 years ago, it gouged out the 386-foot-deep, 16-mile-long depression now known as Jackson Lake.
The receding layers of ice also left other calling cards. Several beautiful glacial lakes were created, including Phelps, Taggart, Bradley, Jenny, String, and Leigh. The sides of Cascade Canyon were polished by receding ice. Glacial lakes, called cirque lakes, were carved at the heads of canyons, and the peaks of the mountains were honed to their present jagged edges. Five glaciers have survived on Mount Moran. The best trail for glacial views is the Cascade Trail, which leads to the Schoolroom Glacier. But you shouldn't walk on the Mount Moran glaciers unless you are experienced and have the proper gear; the terrain is icy and can be unstable.
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