Reflexion 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 that, in dip section, define an asymmetrical basin bounded along the eastern flank by a major listric normal fault with about 3.0-4.5 km 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 Palaeozoic section exploiting regionally recognized Mesozoic decollement surfaces. The Tertiary depocentre, adjacent to this fault, shifted from west to east with continued slippage through time, the greatest movement occurring in the Miocene and post-Miocene. In the strike direction, the valleys are separated into at least two sub-basins 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 sub-basins in a given valley. All the valleys contain Miocene and younger rocks; however, not all sub-basins contain the pre-Miocene section, suggesting a complex scheme of structural development.