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.

Rapid growth on the South Rim fire in Black Canyon of the Gunnison National Park forced immediate evacuations in Montrose County on Saturday afternoon.

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