The Bull Draw Fire, burning in a remote area 12 miles northwest of Nucla, grew to 8,700 acres by Thursday.
Containment remained at an estimated 35 percent.
The estimated date for full containment was Aug. 19.
The fire has been consuming heavy fuels and carrying burning through more resistant fuels such as aspen and pasture, according to the incident team, led by commander Brian Pisarek said.
About 300 personnel were assigned to the fire as of Thursday.
The fire is considered the top priority in the Rocky Mountain region, meaning it would be the first to receive new resources.
By comparison, the Plateau Fire north of Dolores was ranked No. 3, and the Moccasin Mesa Fire in Mesa Verde, No. 6.
The Bull Draw fire continued to be most active on the northern, Mesa County side, where it backed down drainages and crossed Mesa Creek.
As the fire moves into timber, it has the potential for larger uphill runs, the incident team said.
Fuel moisture remains low, and there is still potential for severe fire behavior.
Dry and hot conditions were expected to persist through at least Friday, when there is a slight chance of isolated thunderstorms.
Moderate fire growth was expected Friday. Because the fire crossed Mesa Creek, it is established to make a fast upslope run to the north.
This weekend, structures in the northwestern part of the fire could be at risk as the fire travels northwest and upslope.
On Thursday, crews planned to extend, hold hand lines.
On Wednesday, an additional hand crew assisted hand line construction and efforts to hold the southwest section. Most of the crew activity and engine resources focused on the protecting structures in the northwest.
The Grand Mesa, Uncompahgre and Gunnison National Forests on Wednesday closed about 17 miles of Divide Road.
On Monday and Tuesday, the Bureau of Land Management implemented an emergency closure for the Bull Draw area, including Montrose County Roads S15, S17, R23, Z26, and all BLM roads, trails and land.
Although the fire forced the evacuation of a home and several cabins over the weekend, no structures have been lost, public information officer Kimberlee J. Phillips, of the U.S. Forest Service, said in a press release.
The Minnesota Incident Command System Type 2 Blue Team assumed command earlier this week. It is a more robust, federal team than the state-based Type 3 team that had been in place since July 31. The team is using the Nucla Community Center for fire operations.
The team plans will hold a public meeting at 6:30 p.m. Friday at the Nucla Baptist Church.
Smoke from the Bull Draw and Buttermilk fires continued to impact residents in Delta and Montrose counties, which faced air quality advisories all week.
The Buttermilk FireThe Buttermilk Fire is burning in piñon/juniper vegetation in the rugged Lime Kiln drainage area 15 miles northeast of Montrose in the Red Canyon area.
On Thursday, it was estimated at 746 acres, and containment was 70 percent. Firefighters continued to mop up hot spots.