The SouthInc fire spread quickly along steep, rugged terrain in the Fillmore area amid Sunday's hot temperatures.
But firefighters believed they were getting the upper hand and had stopped the forward progress of the blaze by Sunday evening after it had charred 131 acres.
"Cause of the fire has been determined to be target practice on private property," the Ventura County Fire Department said.
#SouthInc Fire stopped at 131 acres. Cause of the fire has been determined to be target practice on private property. Smoke will still be in the area as firefighters work to clean out small pockets of vegetation. Topography is steep and dangerous. @VCFD @VCAirUnit pic.twitter.com/LniB3nffug— VCFD PIO (@VCFD_PIO) July 15, 2019
Air tankers that were dropping water on the flames have been sent home.
Three firefighters suffered minor injuries battling the flames.
Ground crews are expected to remain on scene for some time putting out hot spots.