The Apple fire has burned over 20,516 acres with no containment, San Bernardino National Forest authorities said, a reversal from an earlier assessment of 12% containment.
The wildfire spread by more than 16,000 acres in less than 24 hours.
The fire’s trajectory appeared to be headed up the side of Mount San Gorgonio, and the U.S. Forest Service has closed the San Gorgonio Wilderness.
No injuries have been reported, but some 8,000 people are under evacuation orders in mountain, canyon and foothill neighborhoods.
The fire was in rugged terrain due to the northern and eastern edge of the fire being in steep hillsides, which is not accessible to firefighting vehicles.
Firefighters continue to work to slow the spread of the fire using all resources available including helicopters, fixed wing air tankers, ground equipment and hand-crews.
Fire activity remained active Sunday afternoon and is expected to remain high, with active fire around the perimeter.
The moisture content of vegetation in the area is at record low levels. This condition, coupled with high temperatures, low relative humidity and the fire’s position on the slope is expected to lead to further growth of the fire, authorities said.
Weather will remain similar to the past few days, with hot, dry conditions. Temperatures should be a couple degrees cooler than yesterday, with low humidity.
Current resources on the fire include 20 hand-crews, 6 Helicopters, 178 Engines, and 19 Water Tenders. A number of air tankers are available to the fire as well. There are also a number of unfilled resource orders, and a number of resources responding which are not yet on-scene, authorities said.