Heavy winds that swept through Black Canyon of the Gunnison National Park on Sunday night started “rapid fire spread” after a relatively slow day of growth, according to fire officials.

The South Rim Fire has burned more than 3,600 acres uncontained since sparking Thursday along the canyon's rim as of Sunday night, and officials Sunday said the fire had started spreading into the canyon itself.

Wildfires have forced evacuations at two U.S. national parks in the West as summer monsoon storms increase lightning in the region.