By Susan Meeker

California is going up in smoke as wildfires continue to burn in mostly dry terrain.

Highway 20 between Williams and Clear Lake is closed and thousands of people have been forced from their homes as the massive Rocky Fire continues to blaze along the lake's northeast front in Lake and Colusa counties.

Firefighters from Colusa to Corning have joined with 10,000 other firefighters battling more than 23 active fires burning across California in what fire officials call an "unprecedented" fire season.

"Tinder-dry conditions from the drought continue to allow wildfires to burn at an explosive rate," said Daniel Berlant, spokesman for CalFire on Tuesday. "Just last week, CalFire crews responded to over 300 new fires."

Berlant said CalFire has responded to more than 4,200 wildfires this year, which is about 1,500 more wildfires than average for this time of year.

With more than 5,000 homes at risk from the Rocky Fire by late Monday, authorities issued mandatory or advisory evacuation notices for more than 13,000 residents, some of whom have trickled into Williams for emergency shelter.

As of Tuesday, the inferno had consumed more than 65,000 acres and is only 12 percent contained, Berlant said.

About 3,200 firefighters are assigned to the Rocky Fire, he said.

In Yuba County, the Francis Fire has burned 29 acres and is close to being contained, officials said.

In the Mendocino National Forest in Glenn County and beyond, firefighters continue to search for and identify fires sparked by lightning from recent storms.

Of the approximately 15 fires burning in the past week, only three on the Upper Lake Ranger District remain active, with the other fires declared either contained, controlled or out, spokeswoman Tamara Schmidt said Tuesday.

The Etsel Fire is approximately 32 acres and is 60 percent contained. It is in the Yuki Wilderness and is burning in heavy timber and brush, she said.

The Boardman Fire is 72 acres and 30 percent contained.

The Deer Fire, burning southeast of Lake Pillsbury, is approximately 100 acres.

It is burning in mixed conifer, she said.

"There are three structures threatened," Schmidt said. "Two engine crews and one Type 1 handcrew are currently working on the fire with the help of various air resources."

As dry conditions and hot temperatures continue, fire officials expect more lightning-sparked wildfires as scattered thunderstorms are forecast in northwestern and the upper north part of California over the next few days.

Colusa and Glenn County health officials warn the Rocky Fire has produced significant smoke, and residents in affected areas should be aware of their local air quality and take necessary precautions.

The Colusa County Air Pollution Control District reports air quality conditions currently are in the good to moderate ranges but said conditions could change quickly from good to unhealthy, which may be the pattern for the next few days.

Smoke from fires produce fine particulate matter that can cause serious health problems including lung disease, asthma attacks and increased risk of heart attack or stroke, health officials said.

Where conditions warrant, people should limit their outdoor activity.

People with existing respiratory conditions, young children and elderly people are more susceptible to health effects from these pollutants.

Air District officials urge residents to follow their doctors' orders when exposed to fire emissions.

(c)2015 the Colusa County Sun-Herald (Colusa, Calif.)