The complex geological and climatic events that significantly altered the landscape throughout the Cenozoic Era impacted the diversification of many North American taxa, including freshwater fishes. Here, I employ an array of phylogenetic analyses using a multiple gene tree approach to address several questions regarding the phylogenetic relationships of the North American cyprinid genus Richardsonius and two other closely related genera, Clinostomus and Iotichthys. I also use divergence time estimates generated using fossil calibrations to qualitatively assess the phylogeographic implications of evolution within and among these three genera. Mitochondrial and nuclear DNA sequences show a sister relationship between Iotichthys and Richardsonius, with Clinostomus being sister to an Iotichthys - Richardsonius clade. Therefore, the currently recognized sister relationship between Clinostomus and Richardsonius is not supported by my analyses. The genera Clinostomus, Iotichthys, and Richardsonius appear to be monophyletic lineages, and the two species within Richardsonius, R. balteatus and R. egregius, appear to be reciprocally monophyletic sister species. Richardsonius balteatus and R. egregius both exhibit phylogeographic structure, and I examined phylogeographic structure within R. egregius using molecular phylogenetic and population genetic methods. Divergence time estimates between genera and species are Miocene and Pliocene in age respectively, and divergence between phylogroups within R. balteatus and R. egregius occurred in the late Pliocene to Pleistocene. Splits between genera and species coincide with documented geological and climatic events, and the deepest divergence within R. egregius appears to have been influenced more by Pliocene or early Pleistocene events than by more recent drainage patterns associated with the latest glacial maxima of the Pleistocene Epoch. Contemporary migration does not appear to occur between eastern and western Lahontan Basin populations
