The Laramide orogeny builds the Rockies
A slab of ocean floor slides flat under North America and lifts mountains a thousand miles inland.
- When
- —
- Duration
- 25 million years
- Known to
- ± 5 million years
- Era
- Cretaceous, Mesozoic
Normally subducting plates dive steeply and raise volcanoes near the coast. Beneath western North America the Farallon plate instead flattens out and scrapes along the underside of the continent, transmitting compression far into the interior and pushing up basement blocks where no mountains should be. The result is the Rocky Mountains, unusually distant from the plate margin, along with the basins between them that hold the region's coal and oil. The mechanism was a puzzle for decades and flat-slab subduction is still the best answer.