When the fire was reported 5 miles east of Glenwood Springs, firefighters found large active flames in the highway’s median before the fire ran up the north-facing slope, U.S. Forest Service spokesperson David Boyd said. The fire grew to about 2 square miles by nightfall.

The cause of the fire was under investigation. It was not immediately threatening any homes and there have not been any evacuations, Boyd said.

The fire broke out on a portion of I-70, the state’s main east-west highway, that runs along the Colorado River. Some rafters and their guides had to be evacuated from the river and hikers were also escorted down the trail from Hanging Lake, a popular destination nearby, the Glenwood Springs Post Independent reported.

Some residents elsewhere in Garfield County have been evacuated because of a 47.3 square mile fire burning north of Grand Junction. It was started July 31 by lightning and is 7% contained.