FLAGSTAFF, Ariz. » A wildfire burning in a scenic Arizona canyon is expected to nearly triple in size as crews scramble to get the upper hand in less rugged terrain.

Fire managers plan to let the flames that have been climbing and swirling about the canyon walls burn through flatter lands and into a sort of catcher’s mitt to the north and the west, Deputy Incident Commander Pruett Small said Friday. That means the fire could grow to nearly 36 square miles if rain doesn’t stop it.

"This is the roughest country in America," he said. "We can’t send firefighters right next to the black and march them up a hill. We have to go around to the top and make a big box."

The goals for fire managers are to protect the 300 structures threatened in Oak Creek Canyon, keep the fire from pushing into the communities of Forest Highlands and Kachina Village to the east, and minimize the potential for flooding.

Fire managers said the blaze has cost $2.2 million to fight as of Friday and might take up to 10 more days to fully control.

Firefighters took advantage of cool and calm weather Friday to carry out plans to choke off the blaze as Memorial Day travelers were forced to alter their travel plans because of the fire.

Hotshot crews marched along a winding highway that is a key front in their effort and set fire to the ground to rob the wildfire of fuel and keep it from crossing the road. Helicopters dropped explosive chemicals in the steepest parts of the canyon that firefighters can’t reach. Crews on the plateau widened lines to the northwest where the fire was spreading.

"There might be a huge spike in size, but we want the public to know we’re controlling the fire," fire spokesman Dillon Winiecki said "We are fighting it on our own terms."

The human-caused Slide Fire started Tuesday and by Friday had burned more than 11 square miles in and around Oak Creek Canyon, a scenic recreation area along the highway between Sedona and Flagstaff that normally would be filled with tourists as Memorial Day approaches. The cause is under investigation, but a campfire has been ruled out, said Coconino National Forest spokeswoman Heather Noel.

Slide Rock State Park is among the destinations that are closed. It is one of the most-visited tourist spots in Arizona, with swimming holes and natural water slides that draw tens of thousands of people during summer months.

Weather conditions for the fire over the next several days look favorable, with increased humidity and a chance of rain. Firefighters have established containment lines around 5 percent of the fire nearest to where it started just north of Slide Rock State Park.

Their work also included creating buffer zones around resorts and homes, putting in a sprinkler system around a fish hatchery in the canyon and quickly knocking down spot fires that escaped the main blaze.

Some 900 firefighters were assigned to the fire Friday.

The fire was moving away from Sedona, but that didn’t ease concerns of business owners who worry the blaze will keep customers away from the premier tourist destination over the weekend.

The Sedona Chamber of Commerce has been fielding hundreds of inquiries via telephone and social media from people wondering if they should still visit during the holiday weekend and inquiring about the air quality, officials said.

Chamber of Commerce President Jennifer Wesselhoff said smoke from the fire has been visible from about 3 a.m. to 9 a.m., but the skies clear up as soon as the sun emerges. She said visitors can still go hiking along more than 200 miles of trails.

Evacuations remain in place for a 2-mile stretch north of Slide Rock, and Highway 89A between Flagstaff and Sedona is closed. The fire was 3 to 3 1/2 miles away from the residential areas of Forest Highlands and Kachina Village, where 3,200 residents remained under pre-evacuation warnings.

No injuries have been reported as a result of the fire. No structures have burned.

Associated Press writers Brian Skoloff, Paul Davenport, Terry Tang and Walter Berry in Phoenix contributed to this report.