Smoke from a fire in Mariposa County that burned more than 7,000 acres in less than 24 hours Sunday and Monday is a concern in Tuolumne County, especially when winds out of the south push smoke and particulate matter pollution north toward Sonora and other Mother Lode foothill towns.

Haze from the fire was evident in Sonora before noon Monday. Afternoon winds began pushing smoke out of the Sonora area but the problem could return, depending on winds, morning and afternoon temperatures, and how large the fire grows.

Staff with Tuolumne County’s Air Pollution Control District and Health Department put out an air quality update before 4 p.m. Monday.

“Local air quality conditions have been impacted by nearby fires today and are forecast to be similar through mid-week,” county staff said in the announcement. “Air quality will be worse in the morning and improve with winds from the west as the day goes on. It is possible that the air quality may reach levels that are unhealthy.”

Ridgelines and canyons in Tuolumne County may trap smoke in some valleys and basins, county staff said.

The deputy air pollution control officer for Tuolumne County said Monday he and other county staff were working with Mariposa County and the California Air Resources Board to bring at least two particulate monitors to Mariposa County and perhaps one to Tuolumne County.

The monitors can measure pollution from wildfire smoke that can be harmful to humans.

“We are talking with people in Mariposa County and the state, but no air quality advisory has yet been sent out for Tuolumne County,” Bill Sandman with Tuolumne County Air Pollution Control District said before noon today in a phone interview. “We want to work with our county public health department if we do put out an advisory.”

The earliest a monitor can be deployed in Tuolumne County is Wednesday, Sandman said. Tuolumne County’s particulate matter monitor is currently down for repair. Two monitors should be operational in Mariposa County by Tuesday. One of those monitors may be sited in Coulterville, which could help shed light on conditions in Tuolumne County.

The blaze in Mariposa County broke out just before 4 p.m. Sunday near Detwiler Road and Hunter’s Valley Road, two miles east of the reservoir called Lake McClure. With highs in the 90s to triple digits Sunday afternoon, the fire quickly blew up and threw out a pyrocumulus smoke column towering thousands of feet in the air, clearly visible from locations 45 miles away including Highway 108, Sonora and Old Priest Grade on Highway 120.

Evacuations were ordered along several roads in the rural area east of McClure, and along Highway 49 south of Coulterville. Cal Fire Madera-Mariposa-Merced Unit had distributed no word on the cause of the fire as of 1 p.m. today.

The blaze is called the Detwiler Fire and as of Monday morning it had burned an estimated 7,100 acres, destroyed one structure and damaged another.

Roseann Scrivens of Los Angeles was trying to keep track of the blaze and efforts to fight it because her mother, Nancy Main, helps run a bed-and-breakfast on Highway 49 in Bear Valley and they were up overnight cutting fire lines.

“I haven’t spoken to her today,” Scrivens said in a phone interview. “She messaged me last night, about 12:30 a.m.”

Bill and Nancy Main run the Mariposa Farmhouse Bed & Breakfast, where no one answered the phone Monday afternoon. Part of their house was built in 1894 and is part of a California Historical Landmark.

Winds were the primary factor pushing smoke up into Tuolumne County on Monday, Sandman said.

“Right now we're getting a northerly drift,” Sandman said. “We're hopefully going to get a little westerly wind later today, coming off the ocean and blowing up into the mountains. A westerly drift will help scour some of that smoke out of Tuolumne County.”

Smoke from wildfires contains pollutants, including particulate matter, that can be harmful to humans, Sandman said.

“Smoke from a fire contains all sorts of different pollutants, including nitrogen oxides and particulate matter, in particular,” Sandman said. “These are not good for people to inhale. It reacts with the body’s defenses. Anybody who had respiratory problems or other health issues, the smoke can exacerbate these existing conditions.”

Sandman said his agency recommends people stay indoors when smoke from the Detwiler Fire is drifting into Tuolumne County. Anyone who has to be outdoors should minimize exercise while smoke is obviously drifting into local communities.

Tuolumne County staff advise that air quality can be judged in part by visibility. For example, if smoke is reducing your visibility to three-quarters of one mile or less, the air quality where you are is hazardous.

If you have visibility of 3 miles to 5 miles, air quality where you are is unhealthy for sensitive groups, including the very young and the elderly. If you have visibility to a distance of 10 miles or more, air quality where you are is good.

Tuolumne County staff said people with health conditions including asthma, lung disease or heart disease should make sure they have medications on hand and are following their caregiver’s instructions.

Signs that smoke from a wildfire may be bothering you include coughing, scratchy throat, irritated sinuses, shortness of breath, stinging eyes, runny nose, chest pains and headaches.

If you are advised to stay indoors, keep indoor air as clean as possible. Tuolumne County staff advise keeping windows and doors closed unless it is extremely hot outside. Run an air conditioner if you have one, but keep the fresh-air intake closed and the filter clean to prevent outdoor smoke from getting in. If you don’t have an air conditioner and it’s too warm to stay inside with the windows closed, seek shelter elsewhere.

While the cause of the Detwiler Fire remained undisclosed, Cal Fire law enforcement officers with the Madera-Mariposa-Merced Unit determined vehicles driving in tall, dead grass caused two other recent wildfires in Mariposa County in late June.

The Ben Fire that started June 28 was caused by a vehicle driving in tall, dead grass, and it burned 630 acres of vegetation across multiple properties. Two days later on June 30 another fire in the Hornitos area near Bear Valley Road was sparked by a vehicle driving through tall, dead grass. That second fire was confined to a patch of roadside grass and brush.

Any person who accidentally starts a wildfire can be held liable for fire suppression costs, which can total millions of dollars when blazes blow up and get big.

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