Some 500 tires and other debris were set on fire on Sunday in the backyards of three properties in the Jurupa Valley, authorities said.
The fire was reported in the 54th Street and Beach Street area at 8:11 a.m., according to the Riverside County Fire Department.
Officials estimated that firefighters would stay on the scene for up to four hours to control the blaze and mop up.
The Riverside Fire Department deployed four engine companies to help county firefighters put out the flames.
No injuries were reported.