Teton Fault

The Teton fault is a normal fault located in northwestern Wyoming. The fault has a length of 44 miles (70 km) and runs along the eastern base of the Teton Range. Vertical movement on the fault has caused the dramatic topography of the Teton Range.

The Teton fault is located in a unique geologic setting. The fault is on the boundary of four major geologic provinces: the Basin and Range, Idaho-Wyoming Thrust belt, Rocky Mountain Foreland, and the Yellowstone volcanic plateau. The Basin and Range province is a region of east-west crustal extension. This province adds tension perpendicular to the fault line causing the fault blocks to move apart. The Idaho-Wyoming Thrust belt is located south of the Teton fault and is a region of thick and deformed crust that prevents the fault from extending farther south. The Rocky Mountain Foreland is located east of the Teton fault and is a region of thicker crust. This section of crust is heavier and adds to the vertical downward force on the hanging wall of fault. The Yellowstone volcanic plateau is a region of uplift and expansion that influences both vertical and horizontal forces on the Teton fault.

The Teton fault is unique in that it dips or slopes to the east. The majority of major faults in the Basin and Range province dip to the west. The unique dip of the Teton fault can be explained by the subsidence of the Snake River Plain. The Snake River Plain is located to the west of the Teton fault and was formed by the migration of the Yellowstone caldera across southern Idaho. As this section of crust cools it tends to subside causing the footwall of the fault to tilt down toward the west.

The Teton fault is also an important feature in a larger region of seismic activity called the Intermountain Seismic Belt. This region extends from western Montana south to northern Arizona.

The development of the Teton fault has been influenced by many past geologic events. In the Precambrian, extensive plutonism caused metamorphism and deformation of the region that would become the Teton Range. During the Mesozoic and early Tertiary, the region underwent compression and crustal thickening. This formed thrust faults and folds. In the Late Tertiary, compressional forces ceased and extensional forces began. This led to the development of the Basin and Range province beginning 20–17 million years ago. The age of the Teton fault is somewhat controversial. Most estimates range between 2 and 13 million years old with a consensus that most of the movement on the fault occurred within the last 2 million years. Rates of movement on the fault have changed throughout time. At the end of the Pinedale glaciation 16,000 to 14,000 years ago, slip on the fault increased. This was likely due to changing stresses on the fault as glaciers melted.

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