Technical Abstract: Few North American legumes are available for rangeland revegetation in the semi-arid western USA. Western prairie clover (Dalea ornata [Douglas] Eaton & Wright) is a perennial legume with desirable characteristics and is distributed in the Great Basin, Snake River Basin, and southern Columbia Plateau. Understanding the genetic and ecotypic variability of this species is a prerequisite for developing populations suitable for revegetation purposes. To address this need, we established two field plots of western prairie clover that originated from 24 sites in Idaho, Oregon, and Washington. Significant variation was detected among the collections for all traits measured. Among the measured traits, flowering time was correlated with collection-site temperature and elevation, which suggests adaptive significance. Genetic population structure estimates from 474 amplified-fragment length polymorphism markers resulted in two distinct, genetically differentiated groups and a third admixed group. These groups also differed in flowering date, inflorescence weight, and plant height. Significant positive correlations were observed between phenotypic and genetic distance matrices (r = 0.35, P = 0.003), phenotypic, and geographic distance matrices (r = 0.35, P = 0.002), and genetic and geographic distance matrices (r = 0.32, P = 0.003). Based on these results, we recommend that two germplasm sources of western prairie clover be developed for use in rangeland revegetation, one from the Deschutes River watershed and the other encompassing the remaining range of collection sites.