The Rocky Mountains rise
A range a thousand kilometres from the coast that made it
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The Rocky Mountains are the chain running from New Mexico into Canada, pushed up between 70 and 40 million years ago. The Laramide orogeny is the standard example of flat-slab subduction, and it explains why the western interior of North America has great uplifted blocks of Precambrian basement pushed up through the sedimentary layers. The process also created the structural traps that later held oil in Wyoming and Colorado, and the uplift finally drained the inland sea that had split the continent in two throughout the Cretaceous.
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The Rockies were pushed up far inland, not at the coast where mountain ranges usually form. The reason is that the ocean plate sliding under North America went unusually flat rather than diving steeply, pressing on the continent far from the edge.
Sources
- USGS: Geologic Provinces of the United States — Rocky Mountains
- Encyclopædia Britannica: «Laramide orogeny»
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