Four firefighters were burned Sunday while battling a Northern California wildfire that threatens 150 homes in the Sierra Nevada foothills.

The four were injured at around 5 p.m. as they fought the hot, active northern end of the 2-square-mile blaze. They were airlifted to UC Davis Medical Center in Sacramento, state fire spokesman Daniel Berlant said.

Two state firefighters and a U.S. Forest Service member were expected to be treated and released. The fourth, also a federal firefighter, had serious but non-life threatening injuries, Berlant said.

He had no details of how the firefighters were injured but said a fire engine was damaged.

The fire erupted Saturday and tore through heavy timber and drought-stricken brush about 45 miles northeast of Sacramento. The area is rural, rugged and steep with homes scattered throughout the trees.

The roads are mainly old, one-lane mining paths, some of them washed out, and some firefighters were having to hike in or be dropped by helicopter, Berlant said.

About 1,100 firefighters, aided by a DC-10 and other aircraft, battled the fire but it was only 15 percent contained Sunday night.

Some 30 to 40 homes in foothill communities, including one belonging to Berlant's parents, were under mandatory evacuation but the flames placed up to 200 homes at risk, ranging from trailers to retirement homes, Berlant said.

"Many of the people live off the grid, they want to be left alone, and they have trees all over the place" which makes it harder to protect them from fire, Berlant said.

The fire didn't expand much throughout the day but there was concern for Monday, when temperatures could start rising toward triple digits and winds could shift and drive flames back south. If that happens, "hundreds and hundreds of additional homes" could be threatened, Berlant said.

The fire was one of about a dozen major blazes that crews were battling statewide. Since Jan. 1, firefighters have responded to some 1,200 more blazes than they typically would face for the period and "as we continue to get deeper into the summer, conditions are only going to be drier," Berlant said.

Meanwhile, firefighters gained ground against a wildfire near Napa Valley wine country, and on Sunday that fire was 65 percent contained.

The Napa-area blaze has burned more than 10 square miles of drought-parched countryside near Lake Berryessa, about 45 miles east of wine country.