We compared genetic diversity and body condition indices among two source locations in Catron County, New Mexico (Whitewater Creek and Middle Fork Gila) and the recipient population (Saliz Creek) to evaluate individual- and population-level fitness responses related to the admixture of gene pools following the the translocation of Mogollon Narrow-headed Gartersnakes (Thamnophis rufipunctatus). Our body condition dataset consisted of 294 snakes, and 174 genetic samples were used for genetic diversity estimates, with 95 snakes sharing both genetic and body condition data used for heterozygosity-fitness correlation analyses. As Thamnophis rufipunctatus is listed as threatened under the Endangered Species Act, sensitive location information can be made available upon request by contacting the dataset point of contact.