My next post about the Geology of the National Parks Through Pictures is from one of the closest National Parks to our house, yet one that we didn't visit because it was so far out of the way from anything.
You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.
|Graphic of the Farallon Plate subducting beneath North America. Image courtesy of the NPS.
Eventually most of the Farallon Plate was entirely subducted beneath North America, especially along the Californian coast, and the compression was released. This essentially allowed North America to expand outwards, like a squeezed sponge being let go. This expansion thinned the crust, while also producing a series of linear mountain ranges and valleys.
|Graphic of the Basin And Range expansion producing linear mountains and valleys. Image courtesy of ISU.edu.
As the expansion progressed, the crust was broken up into a series of smaller blocks. These blocks rotated as the crust stretched out. The rotation of the blocks produced the mountains along the upper corners, with gaps along the lower corners. These gaps eventually were filled with sediment eroded off the mountains, forming the valleys between the mountain ranged.
|Coverage of the Great Basin. Image courtesy of the NPS.
With the thinning of the crust, this area also ended up being lower than the surrounding regions. Because of this water is not able to flow out of the Great Basin, hence the terminology of "basin". Unlike water along the eastern portion of the country and along the west coast, water here does not reach the oceans. All precipitation here eventually ends up in end-basins, such as the Great Salt Lake, where its only outflow is through evaporation.