Ribbon snakes do not get that big....but eastern garter snakes can hit 4 ft. You must also consider that a snake's skin is elongated when it sheds. For example, a 3 ft snake's shed may be 4 ft because it was streched.

Actually, I spotted an eastern garter in my back yard over the weekend. From my experience, they tend to move around a bit more when the weather starts to cool.