Firefighters battled a growing series of fires in northern Mendocino County on Saturday night.

The wilderness fires, which were sparked by lightning Wednesday, doubled in size during the day Saturday and had grown to more than 1,800 acres as of Saturday evening, according to a Cal Fire spokesman. The Lodge Complex fires in the Elkhorn Ridge Wilderness Area, northwest of Laytonville, was 10 percent contained as of 6 p.m. Saturday.

“Firefighters are challenged by steep rugged terrain,” said Cal Fire spokeswoman Julie Cooley.

One structure was reported threatened. Smoke from the fire was reported south in Ukiah.

Dry conditions, low humidity and above normal temperatures also have made it difficult, Cooley said.

More than 800 firefighters from Cal Fire, the Bureau of Land Management, California Department of Corrections and Rehabilitation, National Guard, Laytonville and California Conservation Corps are fighting the blazes. Fourteen bulldozers, four helicopters, 14 water tenders and 51 fire engines have been used to help put out the flames.