How the American West and its Mountain Ranges Formed: New Insights into Plate Tectonics

For years, researchers have puzzled over how the American west was formed--at least where tectonic plates are concerned. Pieces of the puzzle have been either mashed up or are missing. Yet now, scientists have taken seismic images of the deep Earth that reveal features that could lead to the answer as to how the Wild West was created.

The general theory behind the American west was that the mountainous region was formed by the movement of the undersea Farallon plate. The plate slid eastward beneath the continent and dragged island chains along with it. These land masses essentially smashed into and accreted along the west coast. This helped form the mountainous ridges that we know today.

Unfortunately, this theory isn't entirely correct. The latest study reveals that not just one, but several plates had a hand in creating the American west.

The researchers used seismic tomography, also known as earthquake shockwaves, in order to create a 3-D map of the remnants of the others plates that lurk between 500 to 1,200 miles beneath the Earth's surface.

In the end, the researchers made some surprising discoveries. They found that the Farallon plate is actually far smaller than had once been assumed. It actually underwent subduction far west of what was then the edge of North America. There, it ended up colliding with and then subducting under a previously unrecognized oceanic plate. The researchers were able to identify the remnants of several deep-sea trenches that mark these subduction sites.

"The volcanic activity that accompanies the subduction process will have generated lots of new crustal material, which emerged in the form of island arcs along the line of the trenches, and provided material for the crustal blocks," said Karin Sigloch, one of the researchers, in an interview with e! Science News.

They have now dubbed the recently discovered plates the Angayucham and Mezcalera plates. It's possible that they existed beneath an ancient ocean and were eventually overrun by a westward-moving North American plate and eastward-moving Farallon plates, according to the LA Times.

The study could provide answers about the creation and formation of the American west. In addition, it could lead to further research and understanding about exactly what happens beneath our feet.

The findings are published in the journal Nature.