Something Awesome: Keystone Thrust Fault

Unofficial Geology Law #2
If it looks awesome, it probably formed awesomely.
("The Unofficial Law of Awesomeness Causation")


Flying across Nevada in Google Earth, you see something awesome:

(36 07' 03.55"N, 115 31' 24"W)

Two different-colored rocks and a mountain ridge.

To get a better idea of what's going on with that ridge, you can overlay a USGS topo map on top of it:

A ridge! The two different-colored rocks form a ridge.

Zooming in on one section of the ridge, and giving the Google Earth view a little north-facing perspective:

From this perspective, and with the topography data above, we can see that the dark rocks on the left are overlying the white rocks, which form the cliffs on the right.

Now, overlying the USGS Geologic Map of Nevada onto this perspective view:

We see that the two different colored rocks are actually two different geologic units.

Clicking the unit descriptions for these two rock types, we see that the blue unit is Middle Cambrian Limestone, and the green unit is Early Jurassic Sandstone.

From these maps, we've discovered that along this interesting-looking ridge, the older rocks are on top of the younger rocks.

For the record: that's not the way rocks normally work. Normally, old rocks are laid down first, then young rocks are laid on top of them. (That's the Law of Superposition - an Official Law of geology).

You can violate that law with the help of plate tectonics. In this case, with a thrust fault.

This is a classic example of a thrust fault -- the Keystone Ridge Thrust Fault in Red Rock Canyon, Nevada, to be exact. The fault formed ~70 million years ago, during the Sevier Orogeny, and moved the overlying rocks more than 100 km.

1 comment:

  1. hi, Selby!

    hey, if you haven't already, check out a 1984 book by the late Walter Sullivan titled "Landprints: On the Magnificent American Landscape." it's all about his observations of the ground as seen from many airplane flights.

    clear skies,
    Kelly Beatty