East of San Diego near Alpine, the Anderson Truck Trail is the most popular downhill mountain bike ride in the region. This is a long, gnarly, technical downhill run.
To reach the lower trailhead from San Diego, head east on US8 past El Cajon for about 30 miles into Alpine and exit at Harbison Canyon Road (aka Dunbar Lane). Turn left on Peutz Valley Road and park under the bridge.
Ride or shuttle to the upper trailhead by following Peutz Valley Road and turning left on Alpine Blvd into Alpine. Turn left on Victoria and follow to end of road. Enter the trail near the water tower on the right.
The trailhead areas can get very crowded and local residents are getting concerned. Make sure to be extra polite and clean up everything you may see, even if its not your mess. Otherwise, this area may be closed.
Overall, Anderson Truck Trail is the 13th most popular mountain bike trail of all 132 mountain biking rides in California.