Many recent studies have suggested that a majority of the species-level diversification in the arid-adapted North American biota was driven by mountain-building events that took place in the late Neogene (15-2 Ma). This assertion was tested with a phylogeographic analysis of the Odontophotopsis unicornis species-group by using the rDNA internal transcribed spacer regions internal transcribed spacer (ITS)1 and ITS2 and a Bayesian methodology. The validity of the two species in this species-group [Odontophotopsis unicornis Schuster and Odontophotopsis erebus (Melander) ] was tested both morphologically and molecularly. The female of O. unicornis was previously unknown and was associated with the male using molecular data. Here, O. unicornis is described and compared with that of its sister species O. erebus. Divergence dates for the O. unicornis species-group were estimated using the programs r8s and BEAST and calibrated with fossils from Dominican amber. These analyses resulted in a well supported phylogenetic tree that reinforces the notion that O. unicornis and O. erebus are distinct species. Little or no phylogenetic structuring was found among populations of either species. The species in this group seem to have evolved in the middle Pleistocene (≈1 Ma). The lack of phylogeographic structuring in each of the species of the O. unicornis speciesgroup is probably due to the recent origin of these species. This analysis represents one of the few instances of Pleistocene age species-level divergences in desert-adapted taxa.