One of the four major rivers in the Los Angeles Plain, along with the Rio Hondo, Los Angeles, and Santa Ana.
It has an East Fork that is dry, and rough and desert-like, while the West Fork is much more tame and peaceful, in fact the Forest Service has built several fishing stations along the West Fork. Among the more interesting things along the river is the Bridge to Nowhere located in the Narrows of the East Fork that was left stranded in the Los Angeles Flood of 1938.
The West and East Forks of the San Gabriel merge at the San Gabriel Reservoir and after going through the fore mentioned reservoir and the Morris Reservior leave the mountains where it is subjected to channelization, a series of spreading grounds, and two flood control dams (Santa Fe, Whittier Narrows). Most of the water from the mountains is kept above the Whittier Narrows Dam and some of the water is also from reclaimated water.
The San Gabriel Bike Trail also exists. It starts at the other side of the road next to the Angeles National Forest info booth and continues to the end of the San Gabriel in Seal Beach.