Friday Field Foto #80: Thrust fault contact in Nevada
This week’s Friday Field Foto is a close-up view of the Keystone Thrust in southern Nevada.
The key criterion for correctly recognizing a thrust fault is to demonstrate that there are older rocks on top of younger rocks (assuming the whole thing isn’t upside down). In many cases, this isn’t necessarily straight-forward.
What’s great about the Keystone Thrust, at least in this location, is that dark gray Cambrian (540-490 Ma) limestones are on top of bright pinkish and buff-colored sandstones of the Jurassic (200-145 Ma) Aztec Formation. The contact is very easy to see!
Keystone Thrust contact, near Valley of Fire, southern Nevada (© 2009 clasticdetritus.com)
Happy Friday!
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see this older Friday Field Foto for a different view of this same outcrop
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Clastic Detritus 
That’s a neat thrust photo – it makes it look like the contact is irregular rather than smooth, or maybe that’s just the way the limestone erodes. I don’t think I’ve ever seen this thrust before…
“The keystone thrust… is that some sort of maneuver?” –My sister
Awesome photos. Yay geology!
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