SILVERTHORNE, Colo. (KDVR) – Nearly 300 fire personnel have been working to fight the Ptarmigan Fire, which is now 20% contained, fire officials said Friday evening.

The fire, burning northeast of Silverthorne, has burned an estimated 86 acres in terrain that fire officials describe as heavy timber riddled with treacherous downfall and dead-standing trees, according to Summit Fire & EMS.

Alongside the efforts by hand crews to create fire containment lines, structure-protection crews continued to patrol the Hamilton Creek and upper Angler Mountain neighborhoods.

Those neighborhoods, along with the South Forty and Ptarmigan neighborhoods, remain in pre-evacuation status until the risk of fire is minimized. Residents are advised to remain vigilant and be ready to evacuate if conditions change.

Officials said fire activity is expected to continue throughout the weekend and residents may see smoke or visible flames but do not need to call 911.

Residents also are likely to encounter fire personnel and heavy equipment on the roads and should exercise caution. They are asked to leave any firefighting equipment undisturbed and in place.

The entire burn area and the trails leading into it – including the Angler Mountain and Ptarmigan trails – are under a U.S. Forest Service closure.

The cause of the fire remains under investigation.