An out-of-control wildfire that broke out in a forested basin near a Southern California dam triggered the evacuation of about 300 homes late Saturday, authorities said.

The fire, which was reported shortly after 6 p.m. in the Prado Dam Flood Control Basin, quickly spread to at least 175 acres, said Capt. Mike Mohler of the California Department of Forestry and Fire Protection.

He said firefighters on the ground were hampered by difficult access to the raging blaze.

"The fire is fueled by thick brush in a riverbed that hasn't burnt in years," Mohler said. "The fire is creating its own weather, so firefighters are having difficulty getting in there."

He said the flames were about a half-mile north of a residential area along the border of the cities of Norco and Corona. A mandatory evacuation was ordered for about 300 homes in the area.

"The fire is heading toward a populated area," Mohler said.

The fire, visible from State Routes 71 and 91, sent a large plume of smoke that could be seen miles away. The cause of the blaze was under investigation.