About 500 tires and other debris piles ignited Sunday in the backyards of three properties in Jurupa Valley.
The fire was reported at 8:11 a.m. in the area of 54th and Beach streets, according to the Riverside County Fire Department.
Officials estimated that firefighters would remain on the scene for up to four hours containing and mopping up the blaze.
The Riverside Fire Department deployed four engine companies to help county firefighters douse the flames.
No injuries were reported.