Reflection seismic data in the 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 asymmetrical basins each bounded along the eastern flank by a major listric normal fault with about 3.0–4.6 km (10,000–15,000 ft) of displacement. The western flanks are defined by gentle east-dipping ramps. Seismically, the surfaces of the listric faults are interpreted to dip westward and become bedding-parallel within the Paleozoic sequence, perhaps exploiting regionally recognized Mesozoic decollement surfaces. The Tertiary depocenters, adjacent to the faults, shifted from west to east with continued slippage through time, the greatest movement occurring in Miocene and post-Miocene time. In the strike direction, the basins are separated into at least two sub-basins by an east-west, structurally high axis. The axes are postulated to be the result of a tear fault associated with movement along the listric normal fault.

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