Wildfire explodes to more than 79,000 acres

A massive California wildfire has prompted evacuation orders and a highway closure.

The Madre Fire ignited Wednesday afternoon in San Luis Obispo County, according to Cal Fire. It has since grown to 79,630 acres and is 10% contained as of Saturday, fire officials said.

MORE: Wolf Fire in Southern California explodes over 2,400 acres amid dry, windy conditions

The fire -- the largest in California so far this year, according to Cal Fire data -- is burning in a largely rural area in the Los Padres National Forest near Highway 166, officials said.

Evacuation orders were issued near Highway 166 in San Luis Obispo County. The highway is closed from U.S. 101 near Santa Maria to Perkins Road in the New Cuyama area of Santa Barbara County, according to the California Department of Transportation.

All Bureau of Land Management lands in Carrizo Plain National Monument are closed to public access due to the fire, the agency said Thursday.

Approximately 50 structures are threatened, according to Cal Fire.

Officials warned that the fire has a high rate of spread.

MORE: LA fires aftermath: How people are rebuilding after losing almost everything

"With the current weather, terrain, and fuel conditions this fire has seen exponential growth in less than 24 hours in multiple counties surrounding the San Luis Obispo County area," the U.S. Forest Service - Los Padres National Forest said on social media Thursday morning. "Smoke impacts will be far-reaching."

The cause of the wildfire is under investigation.