They look like Red Eared Sliders to me though the red on the head isn't visible to the camera lens; they're not box turtles due to the shape of the shell. Found these two sunbathing on a log in Green Timbers Lake over an year ago. June 27, 2012.
My Birding Gear: Nikon D300s, TC-20EIII, 70-200mm f/2.8 VRII, AF-S II 600mm f/4 D IF-ED
If it looks like a duck, and quacks like a duck, we have at least to consider the possibility that we have a small aquatic bird of the family anatidae on our hands. ~ Douglas Adams