The iconic Golden Gate Bridge in San Francisco disappeared under a cloud of smoke, and the skies above the city had an eerie golden glow from out-of-control fires spreading across California.
The California Department of Forestry and Fire Protection said one blaze that ignited on Saturday in western Yolo County spread over the weekend to neighbouring Napa County.
The fast-moving fire has scorched at least 142 square kilometres of dry brush and threatened more than 100 buildings in ranch land northwest of Sacramento.
No injuries were reported and the exact number of people evacuated was unclear. Smoke and ash was contributing to poor air quality in the San Francisco Bay Area and California wine country.
Hot winds fuelled the massive fire that prompted evacuations in rural northern California and had pushed the flames into a neighbouring county.
Images on social media showed an eerie yellow smoke over the bay city as the fire continued to burn.
Evacuations in Colorado
In Colorado, more than 2500 homes were under evacuation orders as firefighters battled more than half a dozen wildfires around the state.
Most of the evacuations on Monday were due to a 202-square-kilometre wildfire in southern Colorado that authorities believe was lit by humans.
San Francisco sky is bizarre right now. Rayleigh scattering through this cloud is depleting all the blues and leaving us with a sepia sky. pic.twitter.com/weUDCkulsN
— Rick Zuzow (@RickZuzow) July 1, 2018
Two military cargo planes joined civilian aircraft and ground crews battling a southern Colorado fire that had burned across 230 square kilometres and forced the evacuation of more than 2000 homes.
The Air Force Reserve C-130s began flying missions on Monday (local time) from their home at Peterson Air Force Base in Colorado Springs.
The planes were equipped with tanks and pumps capable of dropping 11,400 litres of water or fire-retardant slurry in five seconds.
Gabe Lauderbale, a spokesman with the California Department of Forestry and Fire Protection, said on Monday the hot temperatures and gusty winds were contributing to the fast spread of the blaze, at a rate of four square kilometres an hour, in sparsely populated areas of Yolo and Napa counties.
He said slightly cooler temperatures were forecast later on Monday (local time) but gusty winds that could spread the blaze were also expected.
The National Interagency Fire Center said on Sunday (local time) the summer monsoon should bring enough rain to Arizona, Colorado and New Mexico in early July to reduce the risk of major fires.
But the danger remained high through to the end of July in Utah and parts of California, Idaho, Nevada, Oregon and Washington.