Crews from multiple agencies, led by the U.S. Forest Service, are responding to a fire in the Medicine Bow-Routt National Forest in South Routt County, which in a matter of hours more than tripled in size from 20 to 30 acres to about 100 acres.

The fire has been named the Muddy Slide Fire.

First reported at 3 p.m. Sunday, the fire is believed to be burning only on Forest Service land at this point, but firefighters are assessing what homes and other structures could be in the path of the fire. Aaron Voos, spokesperson for the forest, said hand crews have been requested to assist to fight the fire.

“We’ve got a bunch of crews on order, and we will see which ones we get,” Voos said, adding that these crews could come from nearby states.

The fire is currently being fought from the air with both an air-tanker plane and a tandem-rotor helicopter making drops over the blaze. Voos said crews will be working on this fire for the coming days if not longer, and the initial 100-acre size estimate is “really rough.”

Currently, firefighting efforts are focused on protecting structures that could potentially be in the fire’s path, and there aren’t plans to send large teams of firefighters to fight the blaze on the ground Sunday night.

“We’re looking at possibly one crew to go up there and do some scouting and stuff,” said Kevin Thompson, incident commander with the Medicine-Bow Routt National Forest. “At this point we are just focusing on making sure we know the structure triage and making sure we identify structures at risk.”

The fire is the third reported in the last two days in Routt County, with a wildland fire reported near Steamboat Lake on Saturday, and one within the city limits of Hayden on Sunday afternoon.

The National Weather Service has issued a red flag warning for Routt County each of the last two days, as conditions are ripe for fires to start and spread, especially after a week where Steamboat likely set several new high temperature records.

The cause of the fire is not known at this time, but just before the fire was reported, a small squall with several lighting strikes passed through the area, according to Steve Mills, manager of the Lost Elk Ranch.

The fire has been moving quickly, with large flames visible from an area where fire crews are staging near the Lost Elk Ranch off of Routt County Road 16. The fire has been moving southeast, with firefighters at the staging area saying it had moved significantly since they arrived on scene.

Routt County issued pre-evacuation notices at just after 6 p.m. Sunday for residents in the vicinity of Green Ridge and the South Stagecoach area. These areas are to the east and north of the fire.

Routt County Emergency Operations Director David “Mo” DeMorat said the county’s geographic information system mapping department has identified about 30 structures within 3 miles of the fire, with about 158 total within 5 miles.

“(The pre-evacuation order) does not mean people have to leave yet, but they should be starting to make some kind of arrangements,” DeMorat said.

The county used its alerts system, but only about 21% of county residents have signed up online, and many people, especially in this remote part of southeastern Routt County, do not have landlines.

More firefighters were arriving on scene Sunday night.

“With the fire coming down through here, if the wind shifts, we will set up porta-tanks or engines there,” said Oak Creek Fire Protection District Chief Chuck Wisecup. “The way it is headed down right now, there are probably 50 structures that are threatened.”

Wisecup said crews were inspecting the buildings to assess what kind of mitigation, if any, was needed on those structures.

Crews from the Forest Service, Yampa Fire Protection District and Oak Creek Fire Protection District were initially on scene, but additional help has been requested.

The Platte Canyon Wildland Fire Module, a nine-person, specialized firefighting team based in Bailey, also arrived at the eastern staging area just after 6 p.m. The team was already in the area because fire danger was so high.

“We’re kind of like a hand crew,” said Greg Davis, a firefighter with Platte Canyon. “We’re just going to start looking at houses that we can start prepping and getting ready to burn around.”

Smoke from the fire can be seen for miles, including in Steamboat Springs. When Aaron Tisdale learned of the fire from a Steamboat Pilot & Today story reporting the fire, he got in his truck to check it out.

“I wanted to come see how in danger am I,” said Tisdale, who lives south of Stagecoach.

After viewing the blaze with binoculars, Tisdale said the danger to his home was “enough to not like it.”