Spring Canyon begins at MTRP as easy doubletrack, and becomes windy wide singletrack (more like doubletrack) about a half mile from the park boundary. The pop of the lollipop route is true singletrack, good for all skill levels. Some pushing may be required as it gets pretty steep and loose in a few brief spots.
Park at the East Fortuna parking lot of Mission Trails. Take the northern trailhead heading west and take a right (north) at the intersection which heads towards the freeway bridge. Mission trails ends at the freeway - everything North of here is Spring Canyon.
Continue north up the canyon, sticking to the main trail which roughly follows the dry streambed. Approx 1.6 miles in (measured from the park boundary/freeway) look for a narrow singletrack heading up a canyon to your right (northeast.) Follow this trail up the narrow canyon. At the end it climbs out and turns left for the final climb to the crest. At the top, continue straight, past the access road and follow the singletrack down the otherside until you intersect Spring Canyon again. Continue back (left/south) to the trail intersection, and back to your ride.
Warning - MCAS Miramar is nearby. The suggested route avoids the base. If you choose to venture onto other trails, research the boundaries first and pay special attention to your whereabouts as trespassing on Miramar is frowned upon. Bikes can and reportedly have been confiscated. The border of the base is not well marked apparently, so homework is a must.