(Baird & Girard, 1852)
Contra Costa Co., California. May 5, 2014.
This turtle was one of two observed basking on the edge of a small pond up in the hills. It was a great day for herping; Diablo Range garter snakes (Thamnophis atratus zaxanthus) were gliding around the pond, Red-legged frogs (Rana draytonii) were poking their heads up out of the pond, and I added this turtle species to my lifelist about thirty seconds out of the car.
These turtles have sister species relationships with Blanding’s turtles (Emydoidea blandingii) and European pond turtles (Emys). They have been assigned by various authors to Emys, Clemmys, Actinemys, and Geoclemmys. Most recently they’ve been bouncing back and forth between Emys and Actinemys. My guess is that western pond turtles are likely to stay in Actinemys this time. For a recent and comprehensive review of emydid turtles, see:
Seidel, Michael E. & Carl H. Ernst 2017. A Systematic Review of the Turtle Family Emydidae Vertebrate Zoology 67 (1): 1–122