The Mission Fire was reported around 4:03 p.m. near Mission Boulevard and Crestmore Road in Jurupa Valley.
Fire officials said it had the potential to spread to 75 acres because of ongoing winds.
As of 8 p.m., forward progress of the fire was stopped and mapped at 17 acres and containment of the fire was at 40%.
No structures are threatened. The cause of the fire is unknown.
The Schabarum Fire was reported around 2:50 p.m. near the 17200 block of East Colima Road in Hacienda Heights.
Forward progress of the fire stopped at 4.2 acres around 4:37 p.m., fire officials say. It was initially moving toward homes near Rowland Heights. The Los Angeles County Fire Department had crews on the ground and air resources attacking flames from above.
The cause of the fire is being investigated as possible arson, officials say.
A flare up also erupted in the middle of the burn zone of the Bridge Fire in Wrightwood. The smoke does not pose a threat to containment lines.
Fire breaks out in Hacienda Heights, new flare up erupts in the Bridge Fire amid red-flag conditions
This comes as Southern California expected Santa Ana winds to whip through the region, raising concerns for possible wildfires.