PORTLAND, Ore., Aug 8 (Reuters) - A fast-spreading wildfire threatened 740 dwellings in northern Oregon on Friday after destroying a home and five other buildings overnight in what officials said could be one of the state's worst blazes for years.
About 600 households have already been evacuated from the path of the so-called Rowena Fire, which has almost doubled in size since Thursday and is burning to around 3,400 acres in the scenic Columbia River Gorge.
An additional 140 households near the city of The Dalles, in Wasco County, have been told to be on standby to leave.
Experts say extreme drought in California and unusually dry conditions across Idaho and the Pacific Northwest have exacerbated the annual West Coast fire season, which runs from mid-May to mid-October.
In Oregon alone some 4,600 firefighters are battling a dozen blazes across more than 105,000 acres of forests and grasslands.
"This is shaping up to be one of the more active fire seasons we think we will see in decades," Alisa Cour, a spokeswoman for crews fighting the Rowena Fire, said on Friday.
In neighboring Washington state, some progress was reported tackling a lightning-sparked blaze about 12 miles outside the central city of Ellensburg, which is home to 18,000 people.
That wildfire was 15 percent contained on Friday, compared with 10 percent the day before, said Cory Wall, a spokesman for the Washington Incident Management Team.
Eight homes and 10 other buildings have been destroyed, and evacuation orders remain in effect for about 250 homes, he said.
A separate series of four wildfires raging unchecked on the Collville Indian Reservation in northeastern Washington had grown to about 8,300 acres on Friday. The Devil's Elbow Complex fires were threatening 100 structures, officials said.
In Oregon, Governor John Kithaber visited with firefighting crews on Friday and said the Rowena blaze could be one of the state's worst conflagrations in recent memory.
Cour said fire crews were gaining ground in several areas, and that the blaze was 35 percent contained on Friday, up from zero percent Thursday. In some areas, crews intentionally set controlled burns in an effort to limit its spread, she said.
About 12 miles of U.S. Highway 30 remained closed on Friday.
The Rowena Fire has cost $1 million to fight since it was sparked on a brushy hillside on Tuesday night, according to estimates submitted to the National Wildfire Coordinating Group.
In central Oregon, high winds caused the so-called South Fork Complex of fires to grow 25 percent in the past day, fire crews said on Friday morning.
Several other major fires, including one that had threatened a major power transmission line between Oregon and Idaho, were being gradually contained, according to reports submitted to the National Wildfire Coordinating Group. (Reporting by Courtney Sherwood; Additional reporting by Victoria Cavaliere in Seattle; Editing by Daniel Wallis and Mohammad Zargham)