The fire broke out Wednesday morning at the Soex Textile Recycling plant near Orange and Church.
Investigators say an employee was cutting metal when a spark ignited the grass. Within seconds, two acres of fabric bales went up in a thick cloud of black smoke.
Firefighters will examine the property and review the resources used to put out the flames.
Fire crews have responded to five incidents at the Soex facility in the last few years. Cal/OSHA has also cited and fined the plant for a number of safety violations.