ESTES PARK, Colo. (AP) — A wildfire fanned by gusty winds southeast of Estes Park forced mandatory evacuations in a forested region of Larimer County Tuesday, sending plumes of smoke eastward toward the eastern plains.

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The fire was first reported about 7 a.m. in rugged terrain and triggered evacuations in the Hermit Park and Little Valley areas near Estes Park and, later, southward to the Boulder County line and east of U.S. Highway 36 between Estes Park and Lyons. The Roosevelt National Forest closed areas south and east of the fire.

About 150 firefighters had contained 11% of the 115-acre (45-hectare) blaze by Tuesday afternoon, the Larimer County Sheriff’s Office said.

The cause of the fire was unknown.

Winds gusting to 45 mph (73 kph) fanned the fire slowly eastward. Steep terrain of pine and scrub brush made it difficult for local fire crews to gain access. Evacuation shelters were set up in Estes Park and in Longmont, roughly 30 miles (48 kilometers) to the southeast.

County officials had no immediate reports of structures being damaged. Evacuation notices were sent to hundreds of residents, said sheriff’s Deputy Chris Smith.

The National Weather Service in Boulder said an approaching cold front could bring higher wind gusts to the area late Tuesday but lower temperatures just above freezing on Wednesday.

As of Tuesday night, the size of the fire is 133 acres and is 15% contained.