The High Park fire in Colorado so far had claimed 56,000 acres and destroyed at least 189 homes as of Sunday evening, officials said.
At least one person, a woman, was killed in the wildfire near Fort Collins. Thousands of people were evacuated, and The Denver Post reported smoky conditions in the city of Fort Collins.
Larimer County Sheriff's Office spokesman John Schulz said the sheriff's department has stepped up security at fire zone checkpoints to guard looting.
Crews with about 1,700 personnel battled the fire, which was 45 percent contained early Monday, forestry officials said.
Hot, dry conditions worsened the fire threat.
A spokesman for the federal fighting team, Brett Haberstick, temperatures should be lower Tuesday but the wind could gain strength.
Officials said the Springer Fire has burned almost 1,000 acres in the mountains west of Colorado Springs and was still growing Monday.
A fire burned out of control near the Campo Indian Reservation in southern California, with 200 firefighters, four air tankers and three helicopters attempting to deal with the blaze. Evacuees have been advised to seek shelter at the nearby Golden Acorn casino, which California Department of Forestry and Fire Protection spokesman Daryll Pina said was serving as fire crews' command center, the U-T San Diego reported Monday.
Firefighters in Colorado also fought a 12,000-acre fire near Pagosa Springs and a 200-acre fire near Pueblo.
Six western states in the Great Basin, central Rockies and parts of the central High Plains were under critical fire warnings Monday due to the hot, dry and windy conditions, the National Weather Service said. Red flag warnings were also in effect for northwest Arizona and portions of central Alaska.
Temperatures Monday in the High Park fire region were expected to top 90 degrees, with winds reaching 50 mph on ridge tops and in Poudre Canyon, the weather service said.
Fire crews continued containment and cleanup efforts in New Mexico, where the massive Whitewater Baldy fire had burned more than 296,000 acres. The fire was 80 percent contained.
In Nevada, crews worked a fire that had spread through 22,000 acres on the east side of the Schell Mountain Range, about 20 miles north of Ely.
The fire burned in steep, rugged terrain, and was fueled by trees, sagebrush and grass, officials said.
One home had been destroyed.
Fire officials said the wildfire began Saturday when a Forest Service-prescribed burn jumped out of control.
In Arizona, the Poco fire was burning 6 miles northeast of Young and had covered about 3,200 acres since Thursday.