Friday Field Foto #80: Thrust fault contact in 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!
see this older Friday Field Foto for a different view of this same outcrop