"We assume they were started by one or more individuals," Gray said.
Three of the fires were reported after midnight west of the tracks near Lindaro Street, and five more fires started around 12:30 a.m. between Rice and Anderson drives to the east, Gray said.
Fifteen firefighters quickly contained the fires, which presented a challenge because of the number of blazes and the distance between them, Gray said.
The fires burned an estimated 4,000 square feet of vegetation, Gray said.
The last firefighters left the scene around 1:45 a.m., he said.
There are buildings near the railroad tracks but no structures burned, and no injuries were reported.
Gray said the thick vegetation near buildings in the area is a fire hazard and needs to be trimmed back more often.
There are homeless encampments in the area, and some piles of personal belongings were lost in the fires, Gray said.
Gray said San Rafael police questioned people in the area early Sunday morning, and that the fires stopped after that.
The fires were not accidental or caused by cooking, Gray said.