Two wildfires, sparked by lightning nearly three weeks ago, are threatening to destroy as many as 250 homes in far Northern California.

The lightning-sparked fire complex near the logging and gold mining town of Happy Camp grew dramatically over the past several days. The fire started near Highway 299 just after 4:30 p.m. Sunday and quickly escalated to more than 650 acres, according to state fire spokesman Daniel Berlant.

Many of the homes were under mandatory evacuation orders. Fire officials said a shelter for evacuees was being moved later in the day from Weaverville Elementary School to a Baptist church.

California Governor’s Office of Emergency Services spokeswoman Lilly Wyatt said the fire is also threatening close to 20 businesses and facilities, the town high school and an airport.

Dry conditions in a drought-ridden California, along with the addition of gusty winds, fueled the “Oregon fire,” and crews struggled to contain it because of the steep terrain, Berlant said.

Air crews battled a series of wildfires; even as weather kept skies over the fire in the Klamath National Forest smoky, preventing air drops for much of the last several days. However, clear skies expected into next week should allow planes and helicopters to move freely, Jake Rodriguez, an information officer said.

Low humidity and warm weather kept the fires burning in the Klamath National Forest one mile east of the gold mining and logging town of Happy Camp continue its sweep through steep terrain packed with trees desiccated by the state’s extreme drought, Forest Service spokesman Marc Peebles said.

“These trees are very stressed. They are very dry. Firefighters are seeing burning conditions like they have never seen before or for many years,” Peebles said.

The two largest fires in the complex had burned through about 69 square miles by Friday, an increase of about 20 square miles from a day earlier.

About 400 firefighters were battling the blaze. CalFire spokeswoman Cris Hartman said early Monday that the fire was 25 percent contained.

Crews, meanwhile, were getting the upper hand on another set of fires about 18 miles to the south in the Klamath National Forest that also forced evacuations. The fire was 73 percent contained.