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Montana's Geological History

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The history of Montana certainly did not begin in 1805 with the arrival of Lewis and Clark. Millions of years even before Montana became the meeting place for various native tribes, it was the meeting place for powerful natural forces that sculpted its awe-inspiring landscape. As Norma Tirrell wrote in her book, Montana: "Fire and ice, wind and water, massive glaciers, rivers of molten lava, shallow seas, swamps, and deserts: these are the ancient forces that sculpted the mountains, scoured the plains, chiseled river canyons, scooped out great basins, and nurtured a prehistoric kingdom of dinosaurs."

Geologists estimate that the Rockies began to form about 100 million years ago. Before that time, Montana seems to have been a flat plain, periodically covered with water. Tectonic shifting and the rising action of molten rock pushed up the mountain ranges that now form the Continental Divide, stretching from north to south across the North American continent. Glaciers advanced and retreated across the state during several ice ages. When the last of the large glaciers melted about 10,000 years ago, the ice ages had left an enduring imprint in the form of peaks and valleys, as well as crystal lakes and roaring waterfalls -- for example, in the landscape of Glacier National Park.

Volcanoes also have played a significant role in Montana's geological history. They created the incredible natural area that is now Yellowstone National Park, with its geysers and hot springs. The culminating volcanic blast 600,000 years ago seems to have been the most violent ever to shake the earth; between 1,000 and 10,000 times more powerful than the eruption of Mt. St. Helens in 1980. The explosion sent hot gas and volcanic matter across North America, to a distance of over 1,000 miles. The area underneath the earth's thin crust in Yellowstone Park is still the largest and most active hot spot in the world.

Montana holds infinite interest not only for the geologist, but also for the paleontologist. Jack Horner made perhaps the most significant Montanan discovery thus far in 1978, when he found a fossilized nest of dinosaur eggs and baby dinosaurs. The dynamics and chronology of Montana's geological history have worked together to bring fossils closer to the surface in Montana than in most places, and paleontologists there have made many other amazing discoveries.

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