The Oak Ridge fire burning on more than 1,100 acres of U.S. Forest Service land in Pueblo County is the first on that area of land in more than 100 years, forest officials said Saturday.

“This has allowed the area between the Junkens fire burn scar to the north and the Mason Gulch fire burn scar to the south to become overgrown and dense,” forest officials said in a Saturday update. “If fuels aren’t reduced, it’s not a matter of if fire will occur, it’s a matter of when.”

As of Saturday morning, the Oak Ridge fire was burning on 1,156 acres of land in the Pike-San Isabel National Forests and was still 0% contained. That’s the size of 876 football fields and growing.

The flames grew nearly 50 acres overnight from Friday’s 1,109-acre burn area, and they aren’t expected to stop any time soon.

Although the Oak Ridge fire has grown slower than other Colorado wildfires, fire officials don’t expect the blaze to be contained for nearly a month. The fire’s estimated containment date is July 24.

Containment isn’t the end of the flames — it’s the status of a control line being completed around the fire that can be expected to stop the fire’s spread. A wildfire can continue to burn for days or weeks after being fully contained.

Most of the land north, west and south of the fire is steep and rugged, making it difficult for firefighters to get close to flames and increasing the time it takes for crews to get to safety in the case of increased fire behavior or an accident, officials said in Saturday’s update.

More than 445 fire workers Saturday were working on the next line of defense: constructing indirect fire lines, forest officials said.

Indirect fire lines use natural features such as meadows and rocky areas, trails and roads to box in the fire and remove fuel from the flames to prevent further growth.

“We’re making significant progress in implementing the overall strategic plan of ‘boxing in’ the fire, working directly and indirectly along the fire’s edge,” fire officials said in a 1:45 p.m. update. “All aviation units are flying and continue to coordinate with ground resources on hot spots.”

The Oak Ridge fire is being fueled by fallen timber, grass and 2-foot-deep brush — that is, shrubs, bushes or small trees growing beneath large trees in a forest — fire officials said. Removing what they can from those fuels will give fire crews a better chance at keeping the wildfire away from Beulah and other surrounding communities.

On Thursday, crews finished a handline on the east side of the fire, near Beulah, officials said. They worked to strengthen the containment line Friday and proactively burned some areas between the eastern perimeter line and the fire’s edge.

Burning out those areas allowed firefighters to create and use containment lines in terrain that’s easier to navigate and has less fuel for the fire, according to Forest Service officials. This helps increase the likelihood that the lines will hold.

Sparked by lightning during last week’s thunderstorms, the wildfire was first reported June 22, 3 miles northwest of Beulah.

The flames spread slowly over the weekend but jumped from a small, 5-acre fire to more than 275 acres in less than six hours on Monday.

Forest Service officials expect “very active” fire behavior throughout the weekend, with fire conditions easing in the evening as weather fronts bring moisture into the area.

Most of the fire’s spread will be to the north and west, away from Beulah, Forest Service officials said. Crews will continue to reinforce the fire line along the east perimeter between the flames and Beulah.

Middle Creek Canyon Road remains under a mandatory evacuation order, and homes on Vine Mesa, Cascade Avenue, Pine Avenue and Beulah Highlands Road are on pre-evacuation, fire officials said Friday.

The Pike-San Isabel National Forests are shut down until July 26 from Forest Road 386 to the north to Colorado 78 to the south and Colorado 165 to the west.

Closed trails include South Creek, Second Mace, Second Mace Spur, Silver Circle, Left Hand, Squirrel Creek, Mountain Park, Coupler, Dome Rock and Middle Creek, according to the agency.

Davenport Campground, Second Mace/Squirrel Creek Trailhead, Mingus Cabin, the Nature and Wildlife Discovery Center’s Mountain Campus and Squirrel Creek Interpretive Site also are closed.

A temporary flight restriction is in effect around the fire to give room for fire crews to work.

“Do not fly or operate your own drones in this area, as it will impede firefighting efforts and ground our aircraft,” fire officials said in a Saturday statement.