The Bill Riley Trail is a short little trail on the north face of Mt. Disappointment. The switchbacks at the top and bottom are a little tight for bikes, but might be rideable with some intermediate skills.
In between switchbacks is a great flow section, with quality dirt and great trees, that is a lot of fun. Let off the brakes here and enjoy!
Climb up the Mt Disappointment Road to access this trail, or add it onto a shuttle run down Eaton Saddle Downhill Shuttle
via San Gabriel Peak Trail
for extra credit.