As the western United States heads into fall with its cooler, wetter weather, wildfires up and down West Coast states continue to bedevil communities, drought-wracked natural areas, and worn-out firefighters.

In the foothills of the Sierras northeast of Sacramento near Grass Valley Saturday, a fire quickly spread to 250 acres, destroying two homes and forcing the evacuation of dozens more.

While firefighters were making progress, bringing containment to 20 percent by Saturday night, hot, dry weather and heavily forested land was also working against them, the San Francisco Chronicle reported.

"When it gets into the timber, it's a lot harder to fight," said Daniel Berlant, spokesman for the the California Department of Forestry and Fire Protection.

"We have seen this pattern all year long," Berlant told the Chronicle. "There have been a lot more fires. They start in the grass and spread to the treetops, where there is a lot of fuel due to the dry conditions. Once it's into the tree tops, it's a hard fight."

Firefighters faced similar conditions last weekend battling a 300-acre wildfire near Yosemite National Park.

In Southern California, firefighters coping with high temperatures sought to contain a wildfire that forced people to flee about 30 homes near the Cleveland National Forest, which sprawls over the rugged peaks of the Santa Ana Mountains, straddling the Orange and Riverside county line southeast of Los Angeles.

The fire, which burned through about 2 ½ square miles of dry canyon brush, was only about 10 percent contained, Deanne Thompson, a spokeswoman for the Orange County Emergency Operations Center, said Saturday night.

Both heat and smoke advisories were in effect for the area, with temperatures forecast to reach as high as 107 degrees between Sunday and Tuesday.

More than 700 firefighters, aided by six helicopters and five planes, were battling the blaze. "The fire is making a couple of uphill runs," Orange County fire Capt. Mike Petro said Saturday.

The National Weather Service has issued a Red Flag Warning for southern California. In part, it reads:

...RED FLAG WARNING NOW IN EFFECT UNTIL 6 AM MONDAY FOR THE MOUNTAINS AND ADJACENT FOOTHILLS OF LOS ANGELES...VENTURA...AND SANTA BARBARA COUNTIES DUE TO HOT TEMPERATURES...LOW HUMIDITIES...AND INCREASING INSTABILITY...

...FIRE WEATHER WATCH NOW IN EFFECT FROM 6 AM THROUGH 9 PM MONDAY FOR THE MOUNTAINS AND ADJACENT FOOTHILLS OF LOS ANGELES...VENTURA...AND SANTA BARBARA COUNTIES DUE TO HOT TEMPERATURES AND INCREASING INSTABILITY...

...A PROLONGED HEAT WAVE WILL CONTINUE ACROSS SOUTHERN CALIFORNIA THROUGH TUESDAY. THE HOT TEMPERATURES COMBINED WITH LOW HUMIDITIES...AND INCREASING INSTABILITY WILL BRING THE POTENTIAL FOR LARGE PLUME DOMINATED FIRE GROWTH OVER THE LOCAL MOUNTAINS AND ADJACENT FOOTHILLS TODAY IF FIRE IGNITION OCCURS.

Just south of the Oregon-California border, the Happy Camp Complex fire, which has been burning for more than a month on the Klamath National Forest, has reached more than 108,000 acres. It is 45 percent contained.

Farther north, a new fire started Saturday near Grants Pass, Oregon, in the Onion Mountain area of the Rogue River-Siskiyou National Forest.

The fire is being fought by smokejumpers, rappellers, engine crews, helicopters and air tankers, reports the Mail Tribune newspaper in nearby Medford.

"They were able to hold it in check for a while, but in the mid-to-late afternoon the wind picked up and that changed," Rogue River-Siskiyou National Forest spokesman Scott Blower told the Mail Tribune. "That whole area around Onion Mountain is quite steep, quite rugged…. We do have a road system up there but it is also very brushy."

In its current fire season outlook, the National Interagency Fire Center in Boise, Idaho, reports that above normal fire potential will continue across most of the West Coast states through September.

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Currently, there are nine large fires – five in California, three in Oregon, and one in Montana, the fire center reports. For the year so far, there have 39,323 fires covering 2,824,933 acres.

This report includes material from the Associated Press.