Los Angeles County Fire Department firefighters
worked into the night to tackle the massive BobCat Fire before the expected arrival of warmer and drier weather later in the week. The blaze has burned over 112,000 acres and was 17% contained late Tuesday. The big picture: 75 large wildfires were burning in the U.S. Tuesday, the first day of fall, as cooler weather provided relief to firefighters and improved air quality across the West. The mega-fires have killed at least 36 people and charred more than 5 million acres in Oregon, Washington and California — where 26 people have died, over 7,1000 structures have been destroyed and more than 3.6 million acres have been razed. California Firefighters near Wrightwood tackle the Bobcat Fire on Sept. 20. Photo by David McNew/Getty Images Homes destroyed by the mostly contained Hennessey Fire in Napa, California, on Sept. 15. The fire has burned over 315,000 acres, razed 633 structures and killed five people. Photo: Justin Sullivan/Getty Images A firefighter surveys the burned remains of Berry Creek School in California on Sept. 14. Photo: Josh Edelson/AFP/Getty Images Cars drive along the Golden Gate Bridge under an orange smoke filled sky at midday in San Francisco, on Sept. 9, when air quality was among the worst in the world. Photo: Harold Postic/AFP via Getty Images Oregon A 12-year-old girl gets a free haircut from a hairdresser at the evacuation center at the Jackson County Fairgrounds in Central Point on Sept. 16. Photo: Paula Bronstein/AFP via Getty Images Downtown Portland, Oregon, on Sept. 14. Air quality had improved significantly by Sept. 18. Photo: Robyn Beck /AFP/Getty Images Photo: Robyn Beck/AFP via Getty Images Homeowners survey their property in a neighborhood destroyed by wildfire on in Talent on Sept. 13. Photo: David Ryder/Getty Images A woman drops off donations for residents evacuated from the Riverside Fire at the Clackamas County Fairgrounds in Canby Sept. 13. Photo: Robyn Bec/AFP via Getty Images Washington A seagull flies past cranes on Harbor Island as smoke from wildfires fills the air on Sept. 12 in Seattle. "Most of the wildfire smoke has left western WA," the PS Clean Air Agency tweeted Sept. 19. "Air quality throughout the Puget Sound has reached GOOD. We expect GOOD air quality for the rest of the weekend and well into next week." Photo: Lindsey Wasson/Getty Images Smoke from wildfires obscure the Space Needle and the Seattle skyline on Sept. 12 in Seattle. Photo: Lindsey Wasson/Getty Images Montana A Flathead crew member "digging line around a spot fire on the Callahan Fire," according to the U.S. Forest Service on Sept. 18. Photo: Flathead Hotshots/U.S. Forest Service/FacebooK Idaho Part of Highway 21 between Grandjean and 10 miles outside of Stanley, is closed due to a wildfire in Salmon-Challis National Forest. Photo: U.S. Forest Service/Facebook The Trap Fire was reported on the Sawtooth National Forest on Sept. 14 and is "burning on both sides of Highway 21," the U.S. Forest Service notes. Photo: U.S. Forest Service/Facebook Go deeper: Portland has world's worst air quality as West Coast fires raze 5M acres Editor's note: This article has been updated with more details and images from the fires.