Reflection seismic data in Railroad, Diamond, Mary's River, and Goshute Valleys provide information on their structural development that cannot be deduced solely from outcrop and well data.

These valleys contain Tertiary sediments which, in dip section, define an asymmetrical basin bound along the eastern flank by a major listric normal fault with about 10,000 to 15,000 ft (3,048 to 4,572 m) of displacement. The west flank is defined by a gentle east-dipping ramp. Seismically the trace of the listric fault is interpreted to dip westward and sole into the Paleozoic section exploiting regionally recognized Mesozoic decollement

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surfaces. The Tertiary depocenter, adjacent to this fault, shifted from west to east with continued slippage through time, the greatest movement occurring in Miocene and post-Miocene. In the strike direction, the valleys are separated into at least two subbasins by an east-west structurally high axis. The axis is postulated to be the result of a tear fault associated with movement along the listric normal fault.

Tertiary stratigraphy varies between valleys and between subbasins in a given valley. All the valleys contain Miocene and younger rocks; however, not all subbasins contain the pre-Miocene section suggesting a complex scheme of structural development.

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