Firefighters faced a critical day in efforts to prevent a massive California wildfire from reaching the Lake Tahoe resort region Saturday, fearing that hot, gusty winds could fuel the stubborn blaze.

The Caldor Fire churned through mountains just southwest of the Tahoe Basin, cloaking much of the area in toxic smoke and sending tourists packing at a time when summer vacations would be in full swing ahead of the Labor Day weekend.

Hot winds gusting at up to 35 mph (56 kph) were forecast for Saturday, raising concerns that winds could spread the embers from the tops of bone-dry trees and spark new fires.

“It’s going to be a very pivotal day for us,” said Capt. Stephen Horner, a Cal Fire spokesman for the Caldor Fire.

The fire’s eastern edge was about 7 or 8 miles (11 or 13 kilometers) from the city of South Lake Tahoe and did not advance much overnight thanks to operations known as “backfiring,” where firefighters get ahead of the blaze and burn up fuel so the fire has nothing to ignite, said Horner.

“They did backfiring operations that were nothing short of amazing last night in that area,” Horner said.

The Department of Defense is sending 200 U.S. Army soldiers from Washington state and equipment including eight U.S. Air Force C-130 aircraft to help firefighters in Northern California, the U.S. Army North said in a statement. The soldiers are expected to arrive in California in early September after a week-long training. The C-130s have been converted into airtankers that can dump thousands of gallons of water on the flames.

The Caldor fire, burning since Aug. 14 in the Sierra Nevada, increased slightly in size overnight to about 147,000 acres, or 230 square miles (595 square kilometers) but crews were able to get 19% containment, up from 12% the day before, Horner said.

The Caldor Fire has proved so difficult to fight that fire managers this week pushed back the projected date for full containment from early next week to Sept. 8. But even that estimate was tenuous.

It is one of nearly 90 large blazes in the U.S. Many are in the West, burning trees and brush desiccated by drought. Climate change has made the region warmer and drier in the past 30 years and will continue to make the weather more extreme and wildfires more destructive, according to scientists.

In California, 14 large fires are being fought by more than 15,200 firefighters. Fires have destroyed around 2,000 structures and forced thousands to evacuate this year while blanketing large swaths of the West in unhealthy smoke.

South Lake Tahoe City Manager Joe Irvin issued an emergency proclamation Thursday so the city that’s home to Heavenly Ski Resort can be better prepared if evacuation orders come and be reimbursed for related expenses.

The last time the city declared a wildfire emergency was during the 2007 Angora Fire, which destroyed nearly 250 homes in neighboring Meyers and was the last major fire in the basin.

(AP)