This page includes information about several excellent hiking trails you can explore on your own, as well as organized outings with fellow San Gabriels' supporters and led by knowledgeable wilderness advocates.
Links:
[1] http://www.sangabrielmountains.org/places_visit/west_fork_national_bikeway
[2] http://www.sangabrielmountains.org/places_visit/east_fork_trail
[3] http://www.sangabrielmountains.org/places_visit/san_antonio_creek_falls_trail
[4] http://www.sangabrielmountains.org/places_visit/middle_fork_lytle_creek_trail