UPDATED at 9:44 p.m.: A spokesman for the Utah Division of Forestry, Fire and State Lands told KPCW the fire was 5% contained.
8:40 p.m.: The spokesperson said an air drop of flame retardant a short time ago was having the intended effect on the fire. No additional updates on acreage burned will be available until morning, and though the fire is not under control, no structures are threatened. Highway 40 closed intermittently for flame retardant drops.
7:15 p.m.: The Flatline Fire has burned 85 acres. Park City Fire District, the federal Bureau of Land Management, and the U.S. Forest Service are also on the scene.
6:48 p.m.: No structures or power lines are currently threatened. Crews are using hand tools to "flank" the Flatline Fire and one engine has reached the flames to use water. Mike Eriksson from the state Division of Forestry and State Lands said winds were picking up but conditions were still favorable to contain the fire.
6:29 p.m. Officials confirmed the fire is human-caused and are investigating specifics.
Wasatch Fire crews are working to establish a perimeter around the 15-acre Flatline Fire near U.S. Highway 40.
According to Mike Erickson, spokesperson for the Utah Division of Forestry Fire and State Lands, the cause for the fire that broke out on the Flatline Trail in Wasatch Mountain State Park is still unknown but was not from lightning.
The fire was 0% contained as of 5:30 p.m. Erickson estimated eight engines and 40 firefighters were on the scene. Because of distance from the road, crews have to hike to the blaze to establish a dirt perimeter. An air tanker is on the way to the scene from Cedar City but was still about two hours away.
Eriksson said the fire wasn’t spreading quickly thanks to light winds and green vegetation that hasn’t fully blossomed. He hoped the fire would be extinguished by later tonight.
4:37: Shortly after 4:30 p.m., the Wasatch County Sheriff's Office announced the smoke near U.S. Highway 40 was from a brush fire near the Mayflower construction site and asked the public to avoid the area, but the highway remained open.
No structures were under threat at the time of the announcement.

According to Wasatch County Sheriff's Dispatch Supervisor Carrie Diggs, the first call to report the smoke near U.S. Highway 40 above the Jordanelle Reservoir came in around 3:30 p.m. Sunday, and Wasatch County Fire responded.
KPCW will continue to update this story as more information becomes available.