The Holy Fire, which erupted near Orange County's Trabuco Canyon the previous day, was just 2 percent contained by morning despite fire-retardant drops of more than 19,000 gallons that proceeded overnight.
Around 7 p.m. Tuesday, fire officials said a more accurate acreage was 3,399 - not 4,000 - but containment increased to 5 percent.
Half of the 600 firefighters requested to battle the blaze are available on the ground as the rest have been summoned to assist with other fires raging in the state.
"We are so drawn down in the state that our resources will be coming from further and further away," Orange County Fire Authority Capt. Tony Bommarito said.
No major injuries have been reported. Fueled by bone-dry chaparral and grass, the fast-moving wildfire has claimed one home and two other structures.
Evacuations were ordered in the Holy Jim and Trabuco Canyon areas, as well as the Blue Jay and El Cariso campgrounds.
Lake Forest resident Royce Gould said that his friend's cabin in Holy Jim Canyon was "pretty much charred."
"It looks like a moon up there with some trees, really," Gould said. "It's grey, everything's burnt from the hillsides."
There was also a voluntary evacuation warning for the Highway 74 corridor, west from Lookout Restaurant to Nichols Institute and east of Caspers Park. The area also includes all connecting roads in the community of Rancho Capistrano.
The fire is burning the main divide between Orange and Riverside counties. Residents in Lake Elsinore were told to be prepared just in case they need to evacuate, though the blaze was not directly threatening homes in the city.
"The priority for crews today is to try to stop the fire at that ridge line to keep it from slopping over to the Elsinore side of Riverside," Bommarito said.
Firefighters are battling the blaze amid drought conditions with severely dry vegetation and brush. They are also facing triple-digit temperatures, which is driving down any moisture in the vegetation.
Several residents are prepared to evacuate their homes should the fire continue to spread.
"I have some clothes and water in my van ready if they say to move," Lake Elsinore resident Perla Mazari said.
The cause of the blaze was unknown.
Call center lines have been reopened (951) 736-1811 and an Inciweb account has been established for this incident. #HolyFire Updates will continue to be posted as they become available. https://t.co/VM3YowgsJd— Cleveland NF (@ClevelandNF) August 7, 2018