Part of the Fort Rock system of trails, Red Loop is a nice, long loop that starts right from the Oaklands Town Forest parking lot on 85, just north of 101.
This loop has a lot of great stuff. There is some smoother singletrack, but there are also lots of roots and rock features, in addition to lots of bridges (some sketchier than others), which makes this loop super fun and challenging.
Basically start from the lot (take the bigger trail from the lot), and make sure you just keep right from there to stay on the loop. There are a couple false trails, so be careful of that, and at the northern part of the loop you can hit another loop (Northern Exposure), so at that point you would want to stay left. Eventually, the trail will run back into itself, and, congrats, you made it!