Haze filled the sky east of Clovis Tuesday morning, making it difficult to see the Sierra.
The forest service is burning in an 8,000 foot elevation area that hasn't seen a fire in more than 100 years.
Crews are doing research to determine the effects of wildfire on an ecosystem. Officials say this was the ideal time of year for the burn.
Local allergists say your allergies or asthma can be affected by the smoke.
The air quality in Fresno County was rated as unhealthy for sensitive groups Tuesday.
The fire started last Friday. And will burn 820 acres. The burn will last until Thursday.