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| Snow blankets outcrops of red sediments of the Spearfish Formation (Permian and Triassic) and overlying Sundance Formation (Jurassic) exposed in bluffs along the Belle Fourche River in Devils Tower National Monument. These sedimentary formations dip gently to the west away from the Black Hills uplift (DeWitt and others, 1989; NPS, 2008). |
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