This period of volcanism is not related to the present Yellowstone volcano.Īpproximately 30 million years ago, vast expanses of today’s West began stretching apart along an east–west axis. The Absaroka Range along the park’s north and east sides was formed by numerous volcanic eruptions about 50 million years ago. From the end of the Mesozoic through the early Cenozoic, mountain-building processes formed the Rocky Mountains.ĭuring the Cenozoic era (approximately the last 66 million years of Earth’s history), widespread mountain-building, volcanism, faulting, and glaciation sculpted the Yellowstone area. During the Precambrian and the subsequent Paleozoic and Mesozoic eras (541 to 66 million years ago), the western United States was covered at times by oceans, sand dunes, tidal flats, and vast plains. Rocks of this age are found in northern Yellowstone and in the hearts of the nearby Teton, Beartooth, Wind River, and Gros Ventre mountain ranges. Most of Earth’s history (from the formation of the earth 4.6 billion years ago to approximately 541 million years ago) is known as the Precambrian time.
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