The fire just off the 210 Freeway has scorched about 27 acres. It was first reported around 4:30 p.m. By 6 p.m. fire crews said they had stopped its forward progress.
The fire was mostly restricted to the river bed and no structures were threatened.
The Metro Gold Line was shut down as a precaution.
A second, smaller fire was also burning nearby in the Santa Fe Dam Recreation Area.