We investigated the subspecific identity of a rediscovered population of American martens within the range of a presumed extinct subspecies (Martes americana humboldtensis) by comparing mitochondrial DNA sequence diversity from contemporary individuals within the described ranges of M. a. humboldtensis, nearby ranges of M. a. caurina and M. a. sierrae, and a museum specimen of M. a. humboldtensis. Martens from the rediscovered population shared a haplotype (#2) with the museum specimen. This haplotype was found only in the coastal regions of Oregon and California, suggesting that the rediscovered population represents descendants of a relictual population that previously existed in coastal California. The subspecific boundary between M. a. humboldtensis and M. a. caurina may not be valid, because haplotype #2 was shared between coastal Oregon and coastal California populations and no known contemporary or historical biogeographic barriers prevent north–south movement. Thus, marten populations currently located in coastal forests of California and Oregon should be managed collectively to preserve the connectivity that our data suggest occurred historically. M. a. sierrae differed substantially from both M. a. humboldtensis and M. a. caurina, suggesting marten populations were not a historically genetically homogeneous population and divergence may have occurred in separate glacial refugia.