The fires broke out around 3:45 p.m. Wednesday, with one blaze blackening hillsides near Mare Lane and Gelding Way, just south of the Moreno Valley campus of Riverside Community College. The other fire charred open space around Via Del Lago and Iris Avenue.
The two blazes converged on a ridge and burned south into the Lake Perris Recreation Area, prompting authorities to evacuate and close the campground.
More than 100 firefighters, including crews from the Riverside and Corona fire departments and the Pechanga Indian reservation fire department, worked to contain the brush fire.
The blaze was declared 100 percent contained around 6 a.m. No injuries or damaged structures were reported Anyone with information on the fires are encouraged to call the fire department's Anonymous Arson Tip Line is (800) 633-2836.