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The making of Washington: A Geologic History Draw/color in the six cell table of your mini-poster showing major events that formed WA State: Create Mini-Poster That: 1. Visually shows 6 Major Steps (by region, ex. Eastern WA) that created WA State – make colored drawings. 2. Summarize what happened in each major event in right side column (use headers) 3. Gives a time frame for each major event (Add dates). File location: Public/All/ Hagen Science 9/ Geo History of WA Washington doesn’t yet exist! Edge of North American Continent ends east of Idaho Direction of plate movement 200 million years ago: Pangaea breaks up. North American plate moves westward. 200 More than 50 separate terranes (large blocks of mostly ocean crust) collide & dock against the North American continent. Many of these terranes are “exotic”, having travelled very long distances before colliding with continent. Continent eventually expands 400 miles westward. A volcanic island arc moves toward the continent Volcanic arc pushes against Okanogan sediments: Cascade Mountains formed Erosion of the Okanogan terrane becomes the eastern Washington plateau Columbia Plateau Volcanic eruptions: Giant cracks form in crust and spill lots of lava over the Columbia Plateau Columbia Plateau Basalt (lava) layers pile up to form the Columbia Plateau Erosion of sediments from the Cascades begins to fill the marine basin to the west The Olympic Mountains form by folding of the continental crust and Pacific crust Ice Sheet Snow melt from the Olympic and Cascade mountains forms rivers. The Cordilleran Ice sheet moves southward & blocks the river exits into the Strait of Juan de Fuca. The Ice Sheet reaches its full extent southward and begins to retreat. The Puget Sound basin and Puget lowlands are formed Washington Today
