Genetic studies of amphibians frequently reveal substantial population structure often attributed to historical demographic processes from changing climate and isolation due to imposing geographic features. The Western Red-backed Salamander, Plethodon vehiculum (Caudata: Plethodontidae), is the most widespread and abundant terrestrial salamander in the Pacific Northwest. Using mitochondrial DNA sequence data, we addressed questions regarding the phylogeography of P. vehiculum, testing for the presence of Pleistocene refugia and major rivers as barriers to dispersal. Two major clades were recovered using phylogenetic analyses, a southern clade in the Klamath-Siskiyou region and a northern clade ranging from northern Oregon to southern British Columbia. Moderate levels of divergence between the northern and southern clades were observed, warranting further investigation. The northern populations were not highly differentiated from one another. Genetic data presents 2 possibilities, that of a large recent range expansion after the Pleistocene, or possible high habitat connectivity for these salamanders. While the Columbia River does not appear to have been a barrier to dispersal, populations from Vancouver Island and Washington's Olympic Peninsula contain unique haplotypes, as well as relatively higher levels of genetic differentiation compared to other northern populations. The Olympic Peninsula populations also have lower levels of genetic diversity than any other populations throughout the range. Therefore, P. vehiculum shows parallel and dissimilar patterns relating to its historical distribution and genetic population structure compared to other Pacific Northwest fauna.