The largest fire to strike the Tahoe National Forest this year - the American fire - has now burned an estimated 11,950 acres.
Steep terrain and a forecast calling for higher winds are causing concern that the fire will spread, said Mark Brown, spokesman for the US Forest Service.
"The fire is only 45 percent contained," Brown said this afternoon.
The fire, whose origin is under investigation, broke out 17 miles northeast of the town of Foresthill on Aug. 10 and is spreading to the southeast after making gains to the northeast on Friday, Brown said.
"Right now the fire is burning in some steep canyons at the southeast ridge," said Brown.
No populated areas are threatened, including the nearby Foresthill community
Crews are now hiking two miles into the forest after leaving Deadwood Ridge Road, where the fire in burning to the south.
"They're having some significant containment problems there right now," Brown said.
An emergency closure order is in place for portions of National Forest System lands within and adjacent to the American Fire.
So far, the fire has demanded the use of 1,396 firefighters and eight helicopters.
"I would not be surprised if that number gets bigger," Brown said.
The California Department of Forestry and Fire Protection has supplied roughly 200 of those fire fighters to aid the Forest Service, said Daniel Berlant, spokesman for the agency.
"In the Sacramento region and foothills this is the largest fire we've seen this year," said Berlant.
Berlant said that in the last two days fire activity in the region has increased, and includes a 100-acre fire that forced evacuations in El Dorado County Friday and a 1,000-acre fire in Butte County that also has demanded evacuations.
Several small fires are also burning in Placer County currently, he said.
"Our region has definitely seen an increase in fires and that is only going to continue as we start to see a weather system move into our region that's bringing in some pretty strong winds," Berlant said. "That will increase the fire danger as well as the risk for dry lightning."
Berlant said that fire danger is currently high to extreme in most foothill and mountain areas and that level will go even higher after this weekend as the weather shifts.
Call The Bee's Edward Ortiz, (916) 321-1071. Follow him on Twitter @edwardortiz.