The fire began just after 3:00 pm, on June 19, 2017, in the Holcomb Valley area, northeast of Big Bear.
The Holcomb fire, whose size was last estimated at 850 acres, is not threatening any residences, authorities say.
The San Bernardino County Sheriff's Department said the Baldwin Lake area, the Tanglewood Campground and the nearby dump were being evacuated.
While the cause of the fire is unknown, temperatures in the region Monday hit 89 degrees as a heat wave continued to push through the area.
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More than a dozen Cal Fire airplanes are being used to fight the blaze. The Baldwin Lake community is just south of there. Fire officials said the humidity in the area was low, at 10 percent. There are no containment lines around the fire yet.
18 Engines, 9 Water Tenders, 16 Hand-crews, 1 Dozer, 8 Air Tankers, including tanker 911 (VLAT), 6 Helicopters are assigned to the Holcomb fire.
Holcomb Valley Road - also known as 3N16 - is closed between Highway 18 and Van Dusen Canyon Road - also known as 3N09.
The Pacific Crest Trail is closed from Highway 18 to Van Dusen. An information line has been set up for the fire at 909-383-5688.