(Photo by Bill Harris)
Looking north from the mouth of Rock Canyon the abrupt mountain front illustrates the active extensional fault system. The Wasatch fault is an extensional fault that is still seismically active and dozens of small earthquakes occur along it each year. It is broken into several segments that run from Nephi in the south to the Idaho border in the north. An earthquake occurs when one of the these segments ruptures and displaces. After the mountain building event, throughout the late Jurassic and Cretaceous, western North America began an extensional phase the continues today. As the valleys across Nevada and Utah drop due to extensional faulting water runoff exploits fractures in the mountain fronts to form deep canyons, such as Rock Canyon. This extension has been happening over the past 14 million years.