■ Erratic winds added to the challenges facing firefighters battling California’s largest wildfire.

INDIAN FALLS, Calif. — Erratic winds and the potential for dry lightning added to the challenges facing firefighters battling California’s largest wildfire, one of numerous blazes burning Monday across the U.S. West.

Over the weekend, the massive Dixie Fire merged with the smaller Fly Fire and tore through the remote Northern California community of Indian Falls. The blaze had already leveled at least 16 houses and other structures, but a new damage estimate wasn’t immediately available because flames were still raging in the mountain area.

“Fire behavior has been so unpredictable, it hasn’t been safe for inspectors to go in to work,” said Mitch Matlow, a fire spokesman. “Until things settle down, we won’t know the extent of what’s burned.”

Flames spread in remote areas with steep terrain crews can’t easily reach, Matlow said. Gusty winds also hindered containment efforts and the problem could get worse with the predicted arrival later Monday of pyrocumulus clouds — literally meaning ” fire clouds ” — which can bring lightning and the risk of new ignitions.

Fire officials said the blaze had charred nearly 309 square miles of timber and brush in Plumas and Butte counties, about two hours northeast of Sacramento. It was 22 percent contained and more than 10,000 homes were still under threat.

Authorities were hopeful that improving weather will help them continue to make progress against the nation’s largest wildfire, the Bootleg Fire in southern Oregon. It was 53 percent contained after scorching 640 square miles of remote land. On Monday, an additional crew of Oregon National Guardsmen were sent to help out the more than 2,200 people battling the blaze.

The lightning-caused fire has burned at least 70 homes, mainly cabins, and some 2,000 residences were under evacuation orders.