A deadly wildfire burning in the Sierra National Forest, west of Yosemite National Park, has scorched more than 4,000 acres of dry brush along rugged terrain, and is causing smoky, hazy conditions in Yosemite Valley.

The Ferguson Fire, which ignited late Friday evening, is being fueled by hot conditions and steep terrain, according to fire officials. It was only 2 percent contained as of early Sunday afternoon.

"The fire is burning in a very steep terrain," said Sierra National Forest spokesman Alex Olow. "And given that, there is what we call roll out, which causes embers to roll down, which catches areas that haven't burned yet, and of course they start to burn, which can cause the fire to grow in size."

Olow said high temperatures Saturday evening — hovering near 90 degrees Fahrenheit — also contributed to difficult conditions overnight, and those high temperatures remain a concern for firefighters as they continue to battle the blaze.

"Not only are they fighting a fire where they're getting fairly close and experiencing that heat, but they're also exerting and expending energies in extremely hot weather," he said. "So safety is always a concern for the firefighters."