It’s been more than 24 hours since the Highway 13 fire broke out about 15 miles north of Rifle.

Since early Wednesday afternoon, the fire has ballooned in size to over 500 acres.

Fire officials say the flames aren't threatening any structures at this point, but they continue to attack them aggressively.

Three planes and a helicopter are fighting from the air, supporting the more than 75 firefighters who continue to battle strong winds and rough terrain.

The fire is burning in pinon-juniper and mixed conifer in the west side of an area called Grand Hogback.

“It burned from highway 13 up into the Grand Hogback which is very rough, rugged country,” David Boyd, BLM spokesperson, said. “There are no roads up there so we haven't been able to get firefighters on the ground. we are mostly attacking this fire from the air right now.”

There haven't been any evacuations.

Thursday morning the fire was pretty calm, but as winds pick this evening firefighters expect to see more activity and smoke.

The cause of the fire is still under investigation but officials believe it is human caused.

They say dry conditions are a major factor in what's fueling the flames.