BILLINGS, Mont. (AP) — A fire in a remote area along the Montana and Wyoming border exploded in size on Tuesday, officials said.

The fire was burning on 39 square miles (101 square kilometers), fueled by the area’s sagebrush, grass and juniper trees. Its size was up from about 1 square mile (3 square kilometers) on Monday, the Rocky Mountain Area Coordination Center said.

The county imposed some fire restrictions in July, which commonly occur during summer as the landscape dries. Recent hot weather, winds and low humidity have increased the risk of wildfires in the area, The Billings Gazette reported.

Sheridan County is under a warning for extreme fire danger through Tuesday night.

About 40 people are fighting the fire and officials plan to use aircraft to try to douse the blaze, said Sheridan County Fire Warden Chris Thomas.

The fire started in Montana and winds pushed it into Wyoming.