GEOLOGY OF THE ROCKY MOUNTAINS The Rocky Mountains were formed around 80 to 55 million years ago during an event called the Laramide Orogeny. This was a time when the Pacific oceanic plate was forced beneath the North American continental plate at a very shallow angle. Instead of creating volcanoes near the coast, this unusual subduction pushed massive slabs of crust far inland, crumpling and uplifting them into towering mountain ranges. These mountains stretch over 4,800 kilometers (3,000 miles