In 1969, 17 pronghorn were reintroduced onto Umatilla Army Base in Oregon with no subsequent translocations or immigration into this fully enclosed area. We explored the genetic signature this event left on the population using a combination of microsatellite genotypes and mitochondrial DNA (mtDNA) sequencing data of this population. We compared the present day Umatilla herd to its source population and to a southeastern Oregon population. We found the reintroduced population had sharply lower genetic diversity compared to its source despite its rapid increase in population size following the initial founding event. It is likely the observed loss of diversity and the significant differentiation observed between the Umatilla herd and its source was a function of the low number of founders and stochastic losses of diversity in subsequent generations. We observed significant haplotypic and genotypic differentiation between the reintroduced population and its source (G_ST = 0.063, F_ST = 0.078, p < 0.001) that was approximately 3.5 times that found between the source and the southeastern population (G_ST = 0.018, F_ST = 0.021, p < 0.001). Moreover, 2 rare alleles in the source population were found in high frequency in the translocated population. The founding effect, stochastic shifts in allele frequencies each generation, restricted gene flow, and variance in the segregation of alleles related to a polygamous mating system have contributed to the significant differentiation observed between the Umatilla herd and its source. The results of this study can be applied directly to the management of ongoing translocation activities within Oregon.