Tectonic Evolution of Western North America |
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| ca. 25 MYA - 10 MYA |
| Between 25 and 10 MYA, as the North American Plate passed over the former Pacific Spreading Center, relatively thin crust of the Basin and Range was uplifted by upwelling mantle, and fractured along north-south trends. Basin and Range fracturing ends northward in an area covered by flood basalts. |