One of the current challenges facing conservation biologists is a lack of resolution of species boundaries in threatened groups residing in at-risk areas. This is particularly key for habitats like calcareous outcrops that are known to harbor a high degree of endemic species that may also possess extensive morphological variation. Here, we construct the first time-calibrated phylogeny and evaluate species number of the limestone endemic Mountainsnails (Oreohelicidae), a highly-threatened and phenotypically variable family of land snails from Western North America, using sequence fragments of the mitochondrial gene Cytochrome Oxidase subunit I (COI) from 50 recognized taxonomic species and subspecies. We found four highly supported clades that span wide geographic areas from southern Canada to northern Mexico. Using three species delimitation approaches, we identified a largely concordant set of 16 putative species, which represents less than a third the expected number of species given the current taxonomy and our dataset composition. Our results reveal that this is largely a result of two of the delimitation approaches lumping much of the taxonomic diversity of Oreohelicidae into a single species that possesses remarkable shell form variation and convergence. Moreover, we discuss the suitability of these approaches to delimiting clades with recent divergence, which is not uncommon for limestone endemic fauna and flora. To improve management decisions in montane limestone endemics, our research highlights the need for increased molecular and ecological studies of these isolated and phenotypically variable species.