Two separate vegetation fires in Northern California merged into a single fast-growing wildfire early Wednesday, torching about 50 acres as firefighters battled nearly impossible conditions on mountainsides so steep they reached a 100% incline.

The blaze, dubbed the Mile Post 16 Fire, broke out around 1:30 a.m. in the Gorge area near Mile Post 16 on Highway 96, prompting a massive response from local, state and federal crews.

By Wednesday evening, the fire had scorched about 50 acres and remained 0% contained, burning north of Mill Creek Road, south of Norton Creek, east of Norton Creek Road and west of Highway 96 near the Hoopa Valley Reservation.

Firefighters said the rugged landscape has made the battle especially dangerous.

“Fire suppression efforts are being challenged by extremely steep terrain with slopes ranging from 75% to 100%, numerous rock outcroppings and limited access. These hazardous conditions require firefighters to prioritize safety while implementing suppression strategies,” the Hoopa Fire Department and Office of Emergency Services (HFD/OES) said on Facebook.

Officials have called in reinforcements as crews struggle to gain the upper hand.

“Additional resources have been ordered, including personnel from Hoopa Wildland Fire, the U.S. Forest Service Lower Trinity Ranger District, U.S. Forest Service Division 3, Yurok Wildland Fire, air resources, additional engines, and hand crews,” the agency further said.

The growing wildfire triggered evacuation warnings from the Humboldt County Sheriff’s Office, while officials shut down Hoopa Valley Airport so it could be used as a staging area for firefighting aircraft.

“The Hoopa Valley Airport is closed to all public access today. The airport is currently being utilized as an air operations base in support of the ongoing wildfire incident,” HFD/OES said.

Highway 96 also was closed from Carpenter Lane in Hoopa to north of the Sidehill Viaduct as crews worked to contain the flames.

Wildfires are a recurring threat in Humboldt County, where steep terrain, dense forests and dry conditions can quickly turn small ignitions into major blazes.

In 2023, lightning-sparked fires across Six Rivers National Forest burned more than 50,000 acres, while the devastating August Complex Fire charred more than 1 million acres across seven Northern California counties in 2020.

The latest fire comes just a week after another late-night brush fire scorched about 4 acres near the Nixon Fishing Hole in Hoopa.