All the trails near Forest road 525 are ATV trails so while it is possible to mountain bike it is not pleasant due to the ATV traffic and dust. The closest actual mountain biking off of Boynton Pass road heading from the dispersed camping area east towards Sedona. Start at the Aerie trailhead. Do NOT try to Mountain bike from the Devils Bridge trailhead because all you will do is dodge hikers, ATV's and dust balls! From the Aerie trail head you can go north (harder biking) or east (easier) on the Cockscomb trail. Cockscomb will connect to Aerie trails (left - to make a loop.) Or go strait a the Rupp trail and Girdner (or Two Fence) will take you east into West Sedona near the Lizard Creek trailhead. Signage on these trails is pretty good but sometimes hard to read because of sun fading on the signs.