Contrasting hypotheses for the depositional paleoenvironments of the late Miocene to early Pliocene southern Bouse Formation currently hinder progress toward a consensus on tectonic and paleogeographic reconstructions for the lower Colorado River region. The basal carbonate member of the southern Bouse Formation has been interpreted to record deposition in either (i) a large inland lake isolated from the ocean, or (ii) a transgressive intertidal to subtidal marine seaway. In this study, we analyze sedimentary lithofacies, facies associations, paleocurrents, and architecture of large-scale compound bedforms to develop a comprehensive depositional model. Our paleocurrent data and analyses of bedform architecture and facies association support a tidal origin for the southern Bouse Formation. Our paleogeographic reconstruction constrains the location of marine connection required by paleontological and sedimentary data. Our interpretation provides strong evidence in favor of a tidal origin and requires post-Miocene regional uplift.