Starting at Jackson Lake, I've done the blue loop in the counterclockwise direction. It's a gentle climb up fire road to 7400 feet, followed by singletrack the rest of the way back to Jackson Lake. If you don't like singletrack, an extra car could be left at Vincent Gap or Grassy Hollow.
Adding in an out-and-back along Pinyon Ridge to the Jackson Lake loop makes the total ride about 17 miles. This is the ride featured in the book Mountain Biking the San Gabriel Mountains' Best Trails.
Pictures from 4N56 (orange spur in above map)
Desert view from the end of 4N56
The climb back up to the mountains
Finally back to the pine trees!
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