We studied the population biology of Sonora mud turtles (Kinosternon sonoriense) for 10 yr in an extremely hot and dry desert stream habitat in central Arizona. Adults made up 34.4% of the population. Modeling with Program MARK indicated that both age class (adult vs. juvenile-hatchling) and season contributed significantly to the probability of capture. The presence of exotic crayfish (Orconectes virilis) and age class were significant contributors to turtle survival, supporting the hypothesis that exotic crayfish are important predators on hatchlings. Population density estimates indicated low density over the range of water availability. Both adults and juveniles made long-distance movements along the dry stream bed between pools of water. Males and females were both likely to make long-distance movements and were sometimes absent from the study site for years at a time. In addition to terrestrial estivation in foresummer drought, turtles apparently hibernated on land in winter when standing water was available. Growth fit a von Bertalanffy model very well. We make the first report of growth rates for hatchling K. sonoriense. Growth rates estimated from shell annuli were consistent with similar estimates for older turtles in other studies. Measured growth rates, however, were much higher than annuli-based estimates. In contrast to other populations, we determined that hatchlings and juveniles in our study added 1–3 plastron annuli each year, making age estimation from annuli difficult. Understanding relationships between habitat use, invasive predators, and demographics is essential for effective management of low-density populations.