I grabbed this example of a fault surface in 2008, when my students and I were mapping the details of a transfer zone along a part of the Hurricane fault just east of La Verkin. I find that when non-geologists see this rock, and run their hands over it, they are astonished to learn that the polish and grooving was produced in Nature by faulting, and not ‘machined.’
The Hurricane fault, an active Basin and Range fault, is very well exposed immediately east of Hurricane and La Verkin, Utah. The Rock Canyon Member takes on a beautiful polish where faulted. The polish in this rock is like glass, with striations and fine grooves disclosing slip-line direction conspicuously.
Age & Formation
Canyon Member of the Moenkopi Formation of Triassic age, ~250 Ma.