|Cedar Apple Rust Fungus|
The fungus lives in galls that suddenly sprout orange "spore horns" (seriously) in spring after a cool rain. Boy did they ever. The fungus is unusual in that in needs two host species: apple and cedar. And yes, there are lots of apple trees nearby.
I took a photo of his underside in case anyone catches him again. You can use the markings to help identify individual turtles. Let's call this one Ted. Ted the Turtle. If anyone spots him in the future, take a picture of a belly and let me know.