This 15-mile trail is the premier ride in the upper valley--great sidehill and downhill singletracks, incredible views, and some of the best fall colors around.  From Four Corners, the Sunnyside Trail traverses through the aspen groves on the south face of Red Mountain, with frequent lookouts over the whole Roaring Fork Valley and the Maroon Bells, then descends a long spur through the Starwood subdivision to McLain Flats Road just above the Rio Grande Trail.  The Sunnyside isn't treacherously difficult, neither is it for the faint of heart.
--excerpts from Mountain Biking the Roaring Fork Valley by Richard Compton

From Four Corners at the ridge of Red Mountain.