A sprawling wildfire raging mostly unchecked for over a week in southern Oregon forced firefighters into retreat for a fourth straight day as it expanded to become the state's fifth largest blaze in more than a century, forestry officials said Friday.

The Bootleg fire, the biggest among dozens of wildfires flaring across the tinder-dry landscape of the Western United States, has scorched more than 97,530 hectares (241,000 acres) — an area exceeding the land mass of New York City.

Ironically, heavy smoke shrouding much of the region from the fires may act to slightly blunt the effects of yet another heat wave expected this weekend in the Rockies, extending to parts of Montana, Idaho, Wyoming, Utah and Colorado.