From my limited knowledge, the western part of the North America are apart from the rest of the North America a long time ago, then they collided and joined together, forming the folded mountains called the Rockies!
And I assume this was before Pangaea? Cuz the last time I saw a map of Pangaea, N. America was a single chunk.
after the separation of gondwana and the northern continent i cant remember, the pacific and north american plates collided along the line now known as the rockies, and the collision point caused the crust to rise.
The beginning of the Tertiary coincides with the birth of the Rocky Mountains. The event is known as the Laramide Orogeny (orogeny means "mountain building"). The cause of the Laramide Orogeny reaches back more than 200 million years. At the end of the Triassic period, the great supercontinent known as Pangea began to break apart, and North America began to separate from Europe. Far to the west, the North American crustal plate began colliding with and over-riding the Pacific-Farallon Plate. The collision between the two plates caused the crust to buckle and fold -- just like the fenders of two cars in a head-on collision! This folding started in California and gradually moved its way eastward, finally reaching Colorado about 60 million years ago. During the Tertiary, the stresses caused by the colliding plates to the west forced several Precambrian crustal "wedges" upwards, forming the Colorado Front Range and the Southern Rocky Mountains. In some areas, the mountain building was accompanied by volcanic eruptions and magma emplacement. The uplift and volcanism of the early to mid-Tertiary established the highland that would serve as the headwaters for the Gunnison River. Snowmelt from the Sawatch Range to the east, the West Elk Mountains to the north and the San Juans to the south provided an ample supply of water to what would eventually become the Gunnison Basin. Geologists believe that the modern Gunnison River became established in its current course about 10 to 15 million years ago, just after the last eruptions in the San Juans and West Elks. This coincides with the beginning of a period of rapid uplift of the Great Basin and Colorado Plateau provinces that lie between the Rockies and the Sierra Nevada Range in California. To date, geologists are at a loss to explain the forces behind the uplifting of such an immense region. http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_colorado.html
Ys the North American Plate moved westward and a small slab othe Pacific Plate was forced underneath the North American Plate. This slab the buckled up and folded upwards causing volcanoes along the Rocky Mountains in the process. There is a more detailed explanation, a nice diagram about halfway down the page, and also an explanation about how the Grand Canyon was formed at: http://www.kaibab.org/geology/gc_geol.htm Actually the Rocky Mountains were formed by three different episodes and the Southern Rocky Mountains were formed in a slightly different way. They involved plate tectonic compressing. All of the Rocky Mountains are comprise of several different groups of long ranges. One of the reasons for the development of these ranges was that during the long history of the Rocky Mountains they were at one time covered with glaciers. These glaciers carved out seperate ranges in the mountains.
