The Northwestern Pond Turtle (Actinemys marmorata) is known from several locations along the south fork of the Kern River, in the southern Sierra Nevada of Kern County. In 2019, we began a mark-recapture study on Canebrake Ecological Reserve to evaluate the size and demographic characteristics of this population, as no high elevation sites in the southern Sierra Nevada have been previously studied. We trapped turtles annually for five of the last six years and marked 76 turtles (53 males, 17 females, and six juveniles). The mean carapace length for males was 157.1 mm, for females was 143.6 mm, and for juveniles was 92.0 mm. Most turtles were found to be male, and an exact age could not be assigned (10+ years: 48 males and 15 females). We did find five males, two females, and six juveniles for which we could assign an age, and these were evenly dispersed between 1 and 10 years old. Using a Schnabel estimate, we estimate the population size to be 127 turtles (95% CI = 92–207). Gathering demographic data at this site is often difficult due to changing water levels during wet and dry years and occasional trap interference by large predators.