An ornate box turtle (Terrapene ornata ornata). This time of year they are everywhere. I go out of my way to miss them on the road. I hate senseless road-kill and will do almost anything to keep from killing something that way.
These are innocuous fellows (although I think this one is a female) and they are surprisingly speedy. If you get close to one they will duck into their shell, but just for a moment. If they figure it's safe they will come out and high-tail it for cover. They can really make tracks when they want to.