We examined genetic variation and structure in mitochondrial DNA sequences of sharp-tailed snakes (Contia tenuis) from California and southern Oregon. Maximum parsimony and maximum likelihood analyses distinguish two mitochondrial lineages: a north coast clade restricted to cool evergreen forest along the Pacific Coast; and an interior/south clade widespread throughout California. The southern limit of the north coast clade is congruent with that of several other vertebrate taxa, a historical pattern consistent with a long-term marine embayment. We interpret additional phylogeographic pattern as resulting from either gene flow or incomplete lineage sorting. Genetic, distributional, ecological, and morphological data suggest that north coast and interior/south mitochondrial lineages of C. tenuis are distinct at the species level.