Intermediate to Difficult
Bull Run begins near the Mag 7 trailhead on Gemini Bridges Road's upper end. With a little canyon to your left, the route jumps immediately into a mix of singletrack and slickrock from the right side of the parking lot. About a third of the way into the trail, the canyon rim shifts from your left to your right side. The canyon you're about to witness is far larger than the one you saw before. There's a length of road to navigate after a good bit of trail, and then there's a lot more undulating and ledgy slickrock to cover. The views into the canyon are now just breathtaking.
The majority of motorcyclists park where Highway 313 meets the Gemini Bridges Road at 6000 feet height, towards the top of Getaway. The Bull Run trailhead is located 1.1 mile along Gemini Bridges Road. (The 7-up path will lead you to the Bull Run trailhead if you chose to descend Getaway from the top.)
The Bull Run route comes to an end at Arth's Corner on the Gemini Bridges road, just a few steps from Arth's trailhead. (The trail crosses the road immediately above the Gemini Bridges for those who want to see them.) About a tenth of a mile downhill from the bridges, you can join the Arth's or Great Escape trail.)