Evacuations were underway in Shelter Valley, after a brushfire exploded from 40 to nearly 1,000 acres in about an hour late Saturday afternoon.
By Sunday morning, the wildfire has grown to 2,900 acres and Cal Fire San Diego reported zero containment.
The fire, 12 miles east of Julian near Anza-Borrego Desert State Park, was reported about 5:15 p.m. on the Great Southern Overland, according to Cal Fir.
Motorists first called the California Highway Patrol to report smoke in the area at 4:06 p.m. The agency reported the address as 14925 Great Southern Overland Stage.
By 6:38 p.m., the agency tweeted that the fire had spread to about 1,200 acres. An hour later, Cal Fire reduced the acreage estimate to 800 and added that there was cleared vegetation around 5% of the fire.
Flames destroyed three structures, and about 500 residents had been evacuated from the Butterfield Ranch campground.
The American Red Cross sent volunteers to set up a temporary evacuation point at the Agua Caliente Campgrounds, 39545 Great Southern Overland, while animals were sent to Vallecitos County Park.
OnSceneTV also reported that officials believe that the fire started in Mason Valley when sparks went into vegetation as a man worked on a metal fence post.
Fixed-wing aircraft were called off due to high winds, OnScene said, of up to 30 mph. A wind advisory issued by the National Weather Service is expected to remain in effect until 11 p.m. Sunday for county mountain areas.
Flames, OnScene reported, licked along both sides of County road S-2 and burned up into the Laguna Mountains.
Updated at 7:25 a.m., Sunday, May 2, 2021
City News Service contributed to this report.