Running one mile is such a short distance that there is no real definitive loop. The most viable option for one mile is a simple out-and-back, meaning you start at one point, run a half mile, and then use that same trail to return. This can be done on whatever trail you choose. I'm not going to judge you if you just want to hit one mile, but if you really want to experience the greatness that these trails offer, I would encourage you to try some longer distances.