One of the things I wanted to do before I moved from Utah was to get a nice panoramic picture of the Salt Lake Valley from above Salt Lake City. Here is a shot of the Salt Lake Valley looking south (so east is left and west is right). In the picture the Wasatch Mountains are on the left side of the valley and the Oquirrh Mountains are on the right side of the photo.
The reason for this, besides just being a beautiful valley, was the geological setting of the valley. The Salt Lake Valley holds an important place, geologically speaking, in the landscape of the United States. The valley is the eastern most extension of the region known as the Basin and Range.
|Coverage of the Great Basin. Image courtesy of the NPS.
The Basin and Range extends from the Wasatch Mountains in the east to the Sierra Nevada Mountains in the west. It encompasses the western half of Utah and pretty much all of Nevada, as well as parts of Idaho, Oregon, California, and Arizona.
|Illustration of the plate tectonics of the west coast of North America with the Farallon Plate subducting beneath North America. Image courtesy of the NPS.
The formation of the Basin and Range Province began long ago when a plate known as the Farallon Plate was being subducted under the west coast of North America. This occurred along the Californian coast and south into Mexico.
|Evolution of the western coast of North America going from a subduction zone to a transform plate boundary causing the formation of the extensional Basin & Range Province. Images courtesy of the NPS.
The subduction, where one plate goes beneath another, produced volcanoes in California and other places in the American west, and it also squeezed North America. Around 40 million years ago, most of the Farallon Plate was completely subducted beneath North America. What that did was a few things:
- It released the pressure that was squeezing North America, like someone releasing a squeezed sponge.
- The subduction zone was no longer. In it's place a new plate boundary formed, a transform plate boundary known as the San Andreas Fault.