Three brush fires are burning in steep terrain in Sonoma and Napa counties and one smaller fire in Santa Rosa, Cal Fire said Thursday afternoon.

The Geysers Road fire near Geyserville that started at 4 a.m. is 120 acres, Cal Fire spokeswoman Nancy Carniglia said.

The original 50-acre fire was contained but a 70-acre nearby spot fire is not contained, she said.

The fire is 4 miles up Geysers Road near the Hawkeye Ranch.

Nearly 100 firefighters are at the scene including five engines, four crews, four bulldozers, one tanker and one helicopter, Carniglia said. Winds, which had gusted to 40 mph, subsided to 15-20 mph this afternoon, she said.

The Tar Fire at St. Helena and Tarwater roads north of Santa Rosa began as a 2-acre fire but is now 30 acres and remains uncontained, Carniglia said.

Some structures in the rural area are threatened and local fire agencies are standing by to respond to any structure fires, Carniglia said.

There are six engines, two hand crews, one dozer, one tanker, two helicopters and a air attack spotter plane on that fire, she said. Winds in the area are at 10 mph.

Saint Helena Road in Sonoma County and Spring Mountain Road in Napa County are closed.

A fire in Pope Valley in Napa County started around 11:45 a.m., Carniglia said. The number of acres burning is unknown.

The fire is at Sage Canyon Road near Long Ranch Road.

Santa Rosa firefighters are fighting a blaze on Montecito Avenue near Happy Valley Road, Carniglia said. The fire began at 9:50 a.m. and there are homes in the area.