Accurately delimiting species remains a contentious issue within modern systematic biology despite recent advancements in species delimitation and high-throughput sequencing techniques. In this study, I apply an integrative approach for species delimitation by analyzing morphological and genomic data to elucidate the species limits and evolutionary diversification history of Chuckwallas (Sauromalus), a conspicuous group of lizards of the aridlands of southwestern North America. I also implement a newly developed metric called the genealogical divergence index (gdi), which provides a quantitative rather than qualitative measure to compare of the strengths and impacts of evaluating alternative species delimitation hypotheses. Of the five currently recognized species of Sauromalus, the species limits of the geographically widespread and morphologically variable Common Chuckwalla (Sauromalus ater) are the most uncertain. Given evidence of at least four well-supported mtDNA lineages within S. ater that are largely incongruent with any previous taxonomies based on morphology, I explore and test alternative hypotheses that involve multiple species rather than one widespread species. Phylogenetic and multispecies coalescent-based analysis of my genomic ddRADSeq data confirm the presence of at least two major lineages, peninsular and continental groups, within the widespread S. ater that likely diverged at the vicinity of the head of the Gulf of California in northeastern Baja California. Population membership and principal component analyses (excluding S. varius and S. hispidus) demonstrate there is additional phylogeographic structure within the continental and peninsular lineages. Among the four insular endemic species of Sauromalus associated with the Baja California peninsula, genomic and morphological analyses strongly support the continued recognition of S. varius, S. hispidus, and S. klauberi as unique species. Multivariate analysis of meristic scale counts strongly support the distinctiveness S. slevini, but weaker phylogenetic signal is provided by the genomic data; thus, it is advocated to continue recognizing this species until additional data can be analyzed to confirm or disconfirm the distinctiveness of this insular lineage. My results highlight the need for taxonomic revision within S. ater and additional studies on the demography and biogeography of Sauromalus. Lastly, I demonstrate utility of using an integrative approach when delimiting species.