Large wildfires are Grayson  Prestonburning across the West and causing dangerous air quality in Nevada and California.

The Davis Fire, located between Reno and Lake Tahoe, and three blazes just east of Los Angeles − the Line, the Bridge and the Airport fires − are causing some of the worst air qualities in the region.

Mesquite, Nevada and Scenic, Arizona, which sit across the state line from each other about 80 miles northeast of Las Vegas, have some of the most troubling numbers. Mesquite, for instance, had an air quality index of 225 on Wednesday evening. That's considered "very unhealthy," according to AirNow, a government tool tracking air quality.

The index is measured from 0 to 301 and higher, with lower numbers indicating cleaner air. Reno's index of 49 on Wednesday is considered good, for instance. Boulder City, Nevada, near the Hoover Dam, though, was unhealthy at 168.

Las Vegas had an air quality index ranging between 130 and 170 depending on the time of day Wednesday, with both being considered unhealthy. According to the National Weather Service office in Las Vegas, the three fires in Southern California have made conditions worse, with some residents reporting ash falling from the sky.

Air quality conditions across the United States

Fernando Cervantes Jr. is a trending news reporter for USA TODAY. Reach him at [email protected] and follow him on X @fern_cerv_.