State health officials are warning of bad air quality in southwestern Colorado on Thursday after a wildfire burning in the San Juan National Forest grew to nearly 5,000 acres. The lightning-sparked Spruce Creek fire ignited on May 14 on U.S. Forest Service land about 21 miles north of Mesa Verde, fire officials said. As of Wednesday, the fire was burning on 1,867 acres, according to fire records. The burn area more than doubled overnight, flames jumping to reach 4,962 acres of San Juan National Forest land as lower humidity and warmer temperatures worsened fire conditions. Heavy smoke choked many areas in southwestern Colorado on Thursday morning, especially along Colorado 145c south of Rico to Dolores, according to a Thursday news release from the Colorado Department of Public Health and Environment.