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Geology of National Parks, 3D and Photographic Tours

Steamboat Rock State Park
Steamboat Rock is a mesa of Columbia River Basalt that rises in the middle of the Grand Coulee (now flooded by Banks Lake Reservoir). Note the light-colored granitic rock outcrops along the shore. The Mesozoic granitic rocks formed deep underground in the plumbing of an ancient volcanic arc system. Millions of years of erosion removed overlying strata and brought the earth's surface down to the level of the granitic rocks. They were covered again when the Columbia River Basalts flooded the region in late Tertiary time (Alt and Hyndman, 1994; Schuster, 2005).
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