Many people think affectionately of the Rocky Mountains as a hot chocolate sipping, ski lodge, playground. It is actually a combination of discontinuous mountains strung loosely together in a range of mountains. It extends from the eastern tip of Alaska down through Canada and to Mexico at an impressive 3,000 plus miles.
The Rocky Mountains began as islands. The United States was more or less divided in half by a large seaway that also covered the Great Lakes region or seaway. This main seaway is known as the Western Interior Seaway and/or the Cretaceous Seaway.
These islands are believed to have formed in the mid to late Pennsylvanian geologic time frame. This is when temperatures started to cool; the primary life form was amphibious (which later gave way to reptiles), other marine invertebrates and corals, seed ferns and very large tree like plants called Calamites.
The late Pennsylvanian period is also the first half of the Carboniferous time when coal began to form. It is in the middle (approximately) of the Pennsylvanian period that there was a catastrophic event that not only caused cooling temperatures, but also caused tectonic plate movement. This movement caused some of the island formations.
The surface, both land and sea, of the earth sits on what is called tectonic plates. These plates can move. It is approximately 62 miles or 100 kilometers down to the plate from the surface. Take a look at how far it is from one city to the next. From Kansas City to Denver is about 600 miles. More precisely, it is about 69 miles from Denver to Colorado Springs, Colorado.
If one thinks of a ball that is painted with a thick layer of enamel that has weathered to the point of crackling, the pieces or chips approximates what the plates are. Now consider that those plates float stiffly and independently of each other on the surface of that ball.
Some of those crackled areas are larger than others such that they can be classified by size. The plates on earth are grouped from largest to smallest. These are called Primary, Secondary, and Tertiary. Some smaller ones are called micro-plates but are often included in the larger ones for convenience. Currently, there are about 7 primary plates, 8 secondary and several tertiary plates.
Plates move by crashing into each other (forming mountains) and/or by going under or over each other (subduction). When one plate slides under another, that part of it that went under is destroyed or sent closer to the core of the planet (not necessarily intact). These areas of subduction are generally where one finds faults, trenches and volcanoes.
Plates don’t travel in the same directions. One might be going west while the other goes in a northerly direction. These directions of movement, subduction and crashing together all happened in the formation of the Rocky Mountains. Please keep in mind that the mountains in the Rocky Mountain range weren’t created all at once. There were multiple events that created the mountain range we now know.
The Rocky Mountains are on the North American Plate. This plate encompasses all of North America, Greenland, Cuba, Bahamas, parts of Siberia, Japan, and Iceland. It spans eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. Map.
The rock and soil composition (along with appearances) of the Rocky Mountains was influenced by glaciers, erosion, multiple layers of sediment and existing (ancient) rock layers being thrust up and banged together by multiple plate movements at different times. In a very general sense, this is how the Rocky Mountains were formed.