Teton Interagency firefighters appear to have the upper hand on the Cathedral Group Fire in Grand Teton National Park that grew to cover 40 acres by Thursday.

Firefighters dug a line along the west and northwest flanks of the burned area, enabling the park to open the portage between String and Leigh lakes, a trail around Leigh Lake and a campsite there. Half the fire is contained by such barriers, and the only areas now closed is the Cathedral Group turnout and the fire itself.

“They do seem to have a pretty good handle on it,” Grand Teton spokeswoman Jackie Skaggs said Thursday. “With the extra 20-person crew, that adds more boots on the ground to help with the spot fires.”

The crew arrived from eastern Idaho to help about 40 resident firefighters with the blaze. The terrain around a climbing area known as Boulder City has proved challenging, however.

“There’s a lot of heavy down fuels — old trees that have fallen and mixed in among those boulders — and a lot of duff,” Skaggs said. “Because they are sort of scrambling over that rocky terrain, we’re concerned about their safety — twisting an ankle — and it’s a little bit of a slow process.

“They did make great strides on the forested western and northwestern flanks where they can put in traditional hand lines,” Skaggs said.

The fire has abated to the point a water-toting helicopter might not be used while crews dig line along the northern and eastern flanks and tie the containment perimeter into the boulder field.

Small ponds  — the area is a glacier moraine — aided firefighters with a supply for water lines. The fire was reported Tuesday evening, and an investigator was at the scene Thursday.

“It’s still presumed to be human-caused,” Skaggs said. That is partly because of the popularity of Boulder City and the fact there have been no lightning strikes in the last week to two weeks, she said.

Although fire danger in Jackson Hole is considered moderate, there have been 49 instances this summer of careless campers leaving fires unattended, park officials said. Some have escaped campfire rings, but none has grown to significant size.

The Cathedral Group Fire — the largest wildfire in the country this season and just 90 miles west of Jackson Hole — has not caused any significant smoke or haze in the valley. The Jefferson Fire at the Idaho National Laboratory nuclear site raced through sagebrush steppe Tuesday and Wednesday and burned 109,000 acres.

About 300 firefighters have contained 60 percent of the perimeter around the 70-square-mile burned area, and many of the crews have been demobilized. Repair work on downed power lines to laboratories is to begin today. Diesel generators are supplying the necessary electricity until power is restored.

In Yellowstone National Park, officials have said a small fire in the backcountry was not smoking anymore and appeared to have gone out on its own. It was burning on the east side of Yellowstone Lake south of the East Entrance road.