About 20 Napa County firefighters and five engines have joined in the effort to battle the two major wildland fires that are storming Northern California.

As of Thursday afternoon, the Lick Fire near Gilroy had gobbled up 18,900 acres and was 25 percent contained, according to Napa County Fire Battalion Chief Dave Shew. “There are about 1,700 personnel assigned to fight the fire.”

Meanwhile, more than 200 miles north, 1, 650 fire personnel are trying to get the upper hand on the Moonlight Fire, which has blackened 28,000 acres in Plumas County, near the town of Quincy. The blaze has forced the evacuation of the town of Greenville, Shew said.

The Napa County firefighters will remain in the fires until they are contained.

Although fire season has not ended and wildland fire conditions are high in Napa County, Shew said the absence of the county’s firefighters does not lessen fire protection for Napa County.

The fires are creating smoggy skies in the San Francisco bay and San Joaquin Valley areas.

The Moonlight Fire caused state fire officials to issue a mandatory evacuation order for about 100 homes in the North Arm of Indian Valley and a voluntary order for another 400 homes in the communities of Genesee and Taylorsville, said Mark Beaulieu, spokesman for the U.S. Forest Service.

The blaze destroyed an unoccupied summer home, trailer and small shed, but no injuries were reported from the blaze, Beaulieu said.

Its smoke cast a hazy glow across much of Northern California and the San Joaquin Valley. Local health officials advised people with breathing problems to stay indoors.

With forecasts calling for lighter winds, firefighters hoped to make progress corralling the blaze, Beaulieu said. Eight planes were dropping fire retardant, and eight helicopters were dropping water over the fire.

“We have calmer winds today, and we’re making good progress with the aerial attack on flanks of the fire that are near communities,” he said.

Firefighters took advantage of cooler overnight temperatures to set back fires in Henry W. Coe State Park’s steep terrain and were monitoring the weather to determine if they could continue employing the tactic, CDF spokesman Kevin Colburn said.

“The moisture in the vegetation is critically low, so it will more readily burn. Any kind of embers across the line have the potential to start spot fires,” Colburn said.

The San Joaquin Valley Air Pollution Control District issued an air quality emergency warning Thursday, advising residents in northern and central regions of the valley to limit time spent outdoors to avoid breathing in pollution caused by the Moonlight Fire in Plumas County.

The emergency warning was issued because air quality monitors from as far south as Kings County showed the concentration of pollution in the air was “unhealthy” or “unhealthy for sensitive groups,” air district officials said.

The tiny, airborne particles of soot, ash and droplets of liquid can lodge in the lungs, aggravating respiratory conditions and causing asthma attacks.

“The fire is sending a large plume of smoke down through the valley and elevating particulate readings in some areas,” said the district’s meteorologist Gary Arcemont. “If you smell smoke, you are probably breathing it.”

Smoke from the Moonlight Fire has already affected air quality in San Joaquin, Stanislaus, Merced, Madera and Fresno counties, and may impact counties farther south, officials said. Elevated pollution levels will likely continue through Friday afternoon.

Particulate pollution from another fire burning in Santa Clara county is currently flowing toward Monterey, but could also impact the valley air basin tomorrow if winds shift, the air district said.

Associated Press staff contributed to this report