The Cabin fire grew outside of containment lines in the Sequoia National Forest Wednesday evening, prompting firefighters to hike to its location Thursday morning, the U.S. Forest Service said.
It was estimated to have spread over 800 acres by 5 p.m. Thursday.
Portions of the Golden Trout Wilderness are now closed to protect backcountry travelers.
The fire sparked on July 18 when lightning ignited two trees about 50 feet apart in the Golden Trout Wilderness of the Western Divide Ranger District. The fire was contained to two acres by July 22 and monitored by air. A reconnaissance flight noticed the growth early Wednesday morning.