(Reuters) - An Oregon wildfire that has damaged landmarks in the scenic Columbia River Gorge slowed its push toward evacuated houses near the city of Portland on Wednesday, officials said.

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As dozens of blazes raged across the U.S. West, the so-called Eagle Creek Fire near Portland merged late Tuesday with another blaze, the Indian Creek Fire. The two combined have charred 30,930 acres (12,520 hectares), officials said.

Heavy fire activity was expected to continue through September in much of the West, and through October in parts of the northern Rocky Mountains and California, the National Interagency Fire Center said, citing hot and dry weather conditions as the primary cause.

The Eagle Creek Fire, burning in the Columbia River Gorge, forced hundreds of people to evacuate homes earlier this week in communities east of Portland, including Warrendale, Dodson and Latourell, and sent ash falling on the city itself.

Eighty-one large wildfires covering more than 1.4 million acres (570,000 hectares) were burning in the western part of the United States Wednesday, a day after federal officials said 200 active duty military personnel would help fight the fires.

“It’s very unusual to have this many fires burning this many acres across such a broad area at this time in September,” National Interagency Fire Center spokeswoman Jennifer Jones said.

It is the first time in two years fire officials have turned to the U.S. Department of Defense for assistance, and at a time when the fire season would normally be winding down in many parts of the West.

The Oregon fire, now zero percent contained, has burned one home and four outbuildings, as well as damaging the historic Oneonta Tunnel and hiking trails, officials said.

But firefighters protected the historic Multnomah Falls Lodge and damage was not as bad in the gorge as feared.

“The gorge still looks like the gorge; it’s not a wasteland,” Oregon State Fire Marshal’s Office spokesman Damon Simmons told reporters.

A 15-year-old boy is believed to have started the blaze by lighting fireworks, but the investigation continues and the teen has not been charged, Oregon State Police said.

Authorities said they were seeking to determine when they can lift evacuation orders near Portland.

Montana is battling 28 large fires, the most of any state.

One of those, the Caribou Fire northwest of Eureka, has destroyed 10 homes and forced the evacuation of hundreds of people, said fire information officer Don Simon. It was 10 percent contained.