The geology of the Grand Teton area consists of some of the oldest rocks and one of the youngest mountain ranges in North America. The Teton Range, mostly located in Grand Teton National Park, started to grow some 9 million years ago. An older feature, Jackson Hole, is a basin that sits aside the range.
The 2.5 billion year old metamorphic rocks that make up the east face of the Tetons are marine in origin and include some volcanic deposits. These same rocks are today buried deep inside Jackson Hole. Paleozoic rocks were deposited in warm shallow seas while Mesozoic deposition transitioned back and forth from marine to non-marine sediments with the Cretaceous Seaway periodically covering the area late in that era.
70 million years ago, the Laramide orogeny started to uplift western North America, erasing the seaway and creating highlands. The first part of the Teton Range was thus formed in the Eocene epoch. Large volcanic eruptions from in the Yellowstone-Absaroka area to the north left thick volcanic deposits. A series of glaciations in the Pleistocene epoch saw the introduction of large glaciers in the Teton and surrounding ranges, which at times formed part of the Canadian Ice Sheet. Moraines left by less severe ice ages impounded several lakes, including Jackson Lake.
Read more about Geology Of The Grand Teton Area: Precambrian Deposition, Metamorphism, and Intrusion, Paleozoic Deposition, Mesozoic Deposition, Tertiary Uplift and Deposition, Quaternary Volcanic Deposits and Ice Ages
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