A wildfire that had burned through remote areas in the Sierra Nevada for two weeks crested a ridge on Monday and began descending toward the major population centers along Lake Tahoe.
As the Caldor fire intensified amid dry and windy conditions, thousands of people along the lake’s southern and western shores were ordered to evacuate. Crews of firefighters sped to put out spot fires only miles from South Lake Tahoe, Calif.
Tourists normally swarm the lake on the California-Nevada border in the summer months for boating, fishing, hiking, eating and drinking. But by sunset on Monday, the community seemed to stand still.
On streets that were clogged only hours earlier, shops and businesses — motels, restaurants, supermarkets — were deserted. Roads were empty except for fire engines and television reporters documenting the eerie calm.
It was impossible to know when, if at all, the fire would reach the town. But people did not stay to test the fury of a blaze that fire officials estimate could threaten more than 20,000 structures.
Public safety officials warned that the Caldor fire, the latest to grip California during a particularly unforgiving summer for fire crews in the West, showed no signs of relenting. It had scorched more than 177,000 acres and was 14 percent contained on Monday.
The mandatory evacuation zone extended from Tahoma, Calif., on the western shore of the lake, to the Nevada border. “It was a tense few moments, I think, for our citizens in South Lake Tahoe today,” David Stevenson, the city’s police chief, said during a news conference on Monday evening.
Beginning on Tuesday, almost all national forests in California will be closed through Sept. 17 for public safety reasons. The National Weather Service issued a red flag warning for the northern Sierra Nevada and the southern Cascades, meaning that extremely dry conditions and wind gusts of up to 35 miles per hour were likely to cause wildfires to spread in the mountains.
The warning will remain in effect until 11 p.m. on Wednesday for the area, which was cloaked in haze on Monday. Smoke from the fire had deteriorated the air quality to unhealthy levels, the U.S. Forest Service said.
Firefighters on Monday were battling blazes along a dozen-mile section of an old Pony Express route that connects Gold Rush towns along the thickly forested western slope of the Sierra Nevada. At points, crews drew water from the American River to extinguish spot fires and protect the cabins dotted along Highway 50.
Even at 5,000 feet of elevation, temperatures in the midafternoon were in the 90s, unusually hot for the Sierra. Patches of fire burned on both sides of the road.
In the heart of the fire, the skies were orange and the valleys a dense slate of impenetrable smoke.
Along the granite cliffs that descend to the Lake Tahoe basin, firefighters chased down a spot fire that had ignited on the slopes in the direction of South Lake Tahoe. Firefighters and city officials had hoped that the wall of granite would serve as a protective shield for the communities along Lake Tahoe. But winds carried embers that leaped down the cliffs.
Many evacuees grappled with bumper-to-bumper traffic after several major roads in the area were closed. Photographs showed cars at a standstill on Highway 50, the main artery along the southeastern shoreline of the lake.
Chief Stevenson said he had been stuck for about three and a half hours on Highway 50 on Monday.
“I’m so appreciative that our citizens listened to the warning and the order, and evacuated the city,” he said.
The lake, which is known for its sapphire waters and evergreen-surrounded coves, is particularly popular with vacationers from the Bay Area. It is home to several famous ski resorts and casinos, which are just over the border from South Lake Tahoe in Stateline, Nev. Several concerts that had been scheduled for this week at Harveys Lake Tahoe casino were postponed because of the fire threat.
Although wildfires occur throughout the West every year, scientists see the influence of climate change in the extreme heat waves that have contributed to the intensity of fires this summer. Prolonged periods of abnormally high temperatures are a signal of a shifting climate, they say.
As the Caldor fire threatened Lake Tahoe, the Dixie fire, the largest single-origin wildfire in California history, continued to rage in the northern part of the state. That fire had burned more than 771,000 acres in five counties as of Monday and was about 48 percent contained, according to Cal Fire.
Neil Vigdor and Thomas Fuller