A wildfire possibly started by a vehicle parked on dry grass is raging in the Beaver Dam Mountains of southern Utah and northern Arizona, where it had burned 6,000 acres by Monday.

The fire, 20 to 25 miles southwest of St. George, started on the Utah side of the border about noon Saturday. It burned into Arizona and is now moving north into Utah, threatening a communications site in the mountains, a historic mine and a desert tortoise study plot.Conditions are dangerous because of temperatures that are expected to soar to between 102 and 108 degrees Monday, bone-dry 2 percent humidity and winds at 30 mph.

Officials are investigating how the fire started, said Bette Arial, the Color Country South Zone Interagency Fire information officer. But they suspect it began when a vehicle with a hot catalytic converter parked on grass.

More than 200 firefighters have been attempting to contain the blaze.