Park on the access road on the left just at the corner going down. Climb up the Pass Creek Trail a couple miles to the base of Engineer Mountain. Turn left where the Pass Creek Trail meets the Engineer Mountain Trail just above timberline and jam back down the face of Engineer through spruce, aspen, and meadow. Rejoin 550 just below the truck ramp and pedal 4 quick miles back up to your car. Best ridden after the snow melt and north to south.
Average time is four hours for very good riders, otherwise take a lunch and make it a day.
Park at Bubba's Boards at dawn and make the 50 mile loop by dark. Otherwise you'll need to arrange a shuttle. Ask at Bubba's . This is the epic ride of the San Juan. Park at the Sow's Ear .