Yosemite fire grows slowly, but so does containment

The massive blaze known as the Rim Fire has become California’s four-largest fire ever, at times filling Yosemite National Park with smoke as Labor Day weekend visitors try to enjoy one of America’s natural crown jewels.

Firefighters are making steady progress – containment increased from 35 percent Saturday to 40 percent Sunday – but the conflagration burning for two weeks now has grown to 348 square miles, including about six percent of Yosemite’s backcountry.

"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.

Firefighters have carried out controlled burns around two groves of Giant Sequoia trees – the largest living things on earth, some of which are believed to be 2,000 years old – to clear away debris that could otherwise fuel a fire to such an intensity that it dangerously licks at the trees' crowns.

"We are working very hard to protect that,” said fire incident spokeswoman Leslie Auriemmo. “All the lines are in place so it doesn't go into those groves.”

About 4,800 people are working to put out the fire, including firefighters from agencies across California and some 700 specially trained California prison inmates.

The next few days could be critical as the fire continues to move through inaccessible steep terrain where helicopters and air tankers do their best to slow the spread, officials report.

Meanwhile, the Incident Information System 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.”

The cause of the blaze has yet to be determined, but an illegal marijuana-growing operation may have been involved.

One fire official in Tuolumne County offered a tantalizing clue when he recently told a community meeting that the fire was likely caused by marijuana growers, the San Jose Mercury News reported Friday.

"We don't know the exact cause," said Todd McNeal, fire chief in Twain Harte, a town that has been in the path of the flames. But he told a community meeting that it was "highly suspect that there might have been some sort of illicit grove, a marijuana-grow-type thing."

"We know it's human caused. There was no lightning in the area," he said.

NOAA and NASA satellites show that smoke from California’s Rim Fire has drifted thousands of miles, merging with smoke from agricultural burning in the Mississippi Valley.