DENVER — The Cameron Peak fire just west of Fort Collins exploded to more than 89,000 acres Monday, forcing the U.S. Forest Service to close additional parts of the Roosevelt National Forest in Larimer County and order more evacuations. The fire was just 4% contained.

More evacuations were ordered Monday afternoon after the fire crossed Pingree Park Road. The Larimer County Sheriff’s Office said evacuations were mandatory on Colorado 14 from Stove Prairie Landing to Gateway Park for residents and businesses.

After staying relatively consistent in size after erupting about a month ago, the fire grew quickly over the last couple of days to more than 59,000 acres by Monday morning. It then roared to 89,312 acres — 139.55 square miles — by late Monday afternoon.

Alissa Tanner, a spokeswoman for the federal team managing the fire, said a flight Monday afternoon revealed how much the fire had expanded. The sizzling temperatures, wind and extreme low humidity set the stage for the rapid growth, prompting federal and county officials to warn people to get out of harm’s way as quickly as possible.

“There are definitely a lot of structures that are under threat, some imminent threat, some immediate threat and some further out,” Sheriff Justin Smith said about the growing number of evacuations over an increasingly broad area.

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