The Rio Grande cooter (Pseudemys gorzugi), the westernmost species of the genus Pseudemys, is a riverine turtle native to the lower Rio Grande River basin and its tributaries. Currently, P. gorzugi is under review by the US Fish and Wildlife Service for federal protection. However, very little is known about any aspect of this species' ecology and natural history, posing challenges to the assessment of its conservation status. To fill in these knowledge gaps, we studied female size at maturity, clutch size and mean egg size, correlation between reproductive output and female size, and reproductive seasonality of P. gorzugi from mid-May to mid-August 2018. We captured P. gorzugi on the Black River, New Mexico, using traditional hoop net traps and snorkeling. Of 155 females, 28 contained oviductal follicles and 16 contained shelled eggs. We observed a high proportion of gravid females at the end of May through mid-June, although the egg development cycle may extend into August. Our findings allow for a better understanding of this poorly studied species. Knowledge on seasonality of egg development and deposition can aid management planners in determining appropriate times for implementing protection for nesting females and nesting sites.