Due to the nature of the blaze, firefighters attacked the flames from the ground using bulldozers and water.
The mulch pile is 4 to 5 feet deep and will have to be moved around to make sure the water gets down to the bottom.
Authorities are investigating to find out what sparked the blaze.
The Orange County Fire Authority said they expect to finish mopping up and checking for hot spots by 7 p.m. Friday.
