The evolution of the Miocene-Pliocene strata is divided informally into three phases based on differences in seismic facies, depositional environments, and rates of deposition: (1) 20.6-10.75 Ma (initial deepwater basin fill), (2) 10.75-6.2 Ma (deformation stage), and (3) 6.2-3.8 Ma (delta development).

The initial sedimentary fill into the basin (20.6-10.75 Ma) reflects a deep foreland fill. The basin consisted of folded highs around its flanks and structural lows. Pre-existing bathymetric highs affected the distribution of sediments. Sediments were derived primarily from the west through a series of canyon systems cut between preexisting folds. Depositional systems change regionally from channel-fill and overbank to the west to channel-fill, overbank, and sheet deposits on the eastern margin.

Between 10.75-6.2 Ma, the basin was deformed by a series of rising anticlines, which were underlain by thrust faults. The development of these bathymetric highs segmented the depositional systems. Similar to the underlying phase, canyon systems on the western margin of the basin fed sediment to the basin. Sediments were deposited primarily in channel fill and overbank settings that changed basinward to lobes. The uplifting structures acted as barriers for the turbidite flows; the channel and overbank deposits pinched out on the eastern margin of the basin.

By 6.2-3.8 Ma, significant deltas developed to the north, supplying most of the sediment for the basin. Only minor sediment input came from the west. Deep water deposition occurred in the middle to southern portion of the basin with dominance of channel-fill and overbank deposits. These systems are onlapping onto the distal southern margin of the basin