For the first time since a wildfire broke out around Yosemite National Park, dense smoke has begun to obscure the region's majestic mountain views, park officials say.
The smoke from the two-week-old fire is hampering firefighting efforts.
"I'm in Yosemite Valley right now, and I cannot see the cliffs around me," spokeswoman Kari Cobb said Saturday. "The wind has shifted and smoke is impacting the entire park. We have been lucky until now."
All the campgrounds in the Valley still were full as of Saturday morning, despite the thick blanket and burning smell that permeated the area and was expected to linger until at least Monday, she said.
About 8% of the park is inside the fire perimeter.
As a health precaution, visitors were being asked to scale back their outdoor recreation plans and avoid strenuous activities or even stay indoors.
For this weekend's Labor Day traffic, park officials expect about 4,000 cars a day to pass through the gates, down from the normal 5,000 to 7,000 cars for a typical holiday. Some nearby mountain communities have also had a drop-off in business.
Meanwhile, firefighting aircraft were grounded most of the morning because of low visibility caused by the smoke, U.S. Forest Service spokesman Mark Healey said. The blaze had scorched 348 square miles of brush, oaks and pines and 11 homes, as of Saturday, an area larger than the cities of San Francisco, Oakland and San Jose combined.
Of that total, 94 square miles of wilderness have burned in the northern section of Yosemite, up from 75 square miles a day earlier. The fire is 40% contained.
"Despite firefighters' efforts, the remote Rim Fire burning near and in Yosemite National Park continues to be very active," the California Department of Forestry and Fire Protection said in a statement Saturday morning.
"Inaccessible steep terrain and extreme fire behavior" have made suppression efforts difficult, the Incident Information System, which reports fire details, said in a statement. "Continued warmer and drier weather is forecasted for the next several days, which will elevate control concerns and slow burnout progress."
Nearly 5,000 fire personnel are now battling the flames of the Rim Fire. Costs to contain the blaze could reach $47 million.
Since much of the fire is in rough, remote terrain, firefighters are using equipment such as helicopters and air tankers to attack it from above, said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection.
"It is still burning, although we are making progress at the same time," Berlant said.
More than 1.4 million gallons of water have been dropped, as well as more than 1.7 million gallons of fire retardant.
Firefighting assistance has come from 41 states and the District of Columbia. More than 500 California inmates, who have been trained to fight fires, are also working to contain the blaze, Berlant said. These are "low-level," non-violent criminals, he said.
The Rim Fire is the largest U.S. blaze in 2013 and the fifth-largest fire in California history, according to the Incident Information System.
Across California, more than 8,000 firefighters are currently battling six major wildfires.