A California highway is open after being shut down for two days due to a serious air quality problem.

The road reopened Saturday after being closed for several days due a fire in an area known as “the black hole,” a California Highway Patrol official said.

The fire, which started Thursday morning, was reported by the California Department of Forestry and Fire Protection.

The department says it’s investigating the cause.

Fire officials say the cause of the fire is still under investigation.