ESTES PARK, Colo. -- Arson investigators have determined fires that damaged two buildings at Bear Lake were set deliberately, a Rocky Mountain National Park spokeswoman said Wednesday.

The fires caused about $600,000 in damage to a building housing restrooms and a visitor kiosk at the lake, about 10 miles from the park entrance near Estes Park, park spokeswoman Kyle Patterson said.

"We know that it was intentionally set so we know it is arson," she said.

Each building was set afire separately, either late on Monday or early Tuesday, she said. Visitors saw the flames shortly after 7 a.m. Tuesday and alerted a snowplow driver who contacted authorities.

FBI investigators have gathered evidence, but have not determined how the fires were set, Patterson said.

The buildings were made of stone and cedar. Patterson said they planned to close the area temporarily to clean up the debris.

The park is open 24 hours a day year around, although some areas are inaccessible in the winter.

The Earth Liberation Front claimed responsibility for burning down Vail's Two Elk Lodge in 1998 to protest the ski area's expansion into what ELF called lynx habitat. The blaze did an estimated $12 million in damage. The lodge was later re-built.

FBI spokeswoman Ann Atanasio said there is no indication the Park fires were eco-terrorism. Agents were called in because the fires occurred on federal land.

The buildings were made of stone and cedar. Patterson said they plan to close the area temporarily to clean up the debris.