Red Rock Thrust Fault
September 27, 2006
A “thrust fault” is a break in the Earth's crust from squeezing or compression; the block of crust on one side of the fault block moving up the fault plane and overtopping the block on the other side of the fault. Adjacent to the red sandstone Calico Hills in the Red Rock Canyon of Nevada, lies a spectacular example of a thrust fault, the Keystone Thrust. Here 500 million year old limestone rests on 180 million year old sandstone, forming Turtlehead Peak, pictured above.
At the time the thrust fault occurred, the crust here consisted of 180 million year old red and tan sandstone overtopping 500 million year old limestone and dolomite. These layers formed from sandy and calcareous deposits in shallow seas. About 65 million years ago, this crust was compressed causing an oblique fault. A block of sandstone and underlying limestone was thrust on top of a similar block, causing an alternating mountain of sandstone on limestone on sandstone on limestone. Over the next several million years, the upper sandstone was exposed to the elements and eroded away, leaving older limestone (500 million years old) atop younger sandstone (180 million years old), the Keystone Thrust. Photo taken on April 5, 2006.