Wildfires rage in West, may threaten Native American site LOS ANGELES (Reuters) - Wildfires, including one that could threaten Native American archaeological sites in New Mexico, raged across the western United States on Monday as dry weather and gusty winds stymied firefighters' efforts to tame the blazes. In southern California, 2,000 people remained out of their homes as evacuation orders stayed in place for a brushfire north of Los Angeles that has spread to 30,000 acres and destroyed six homes since it erupted last Thursday. In New Mexico, two smaller fires raged out of control in separate wilderness areas including one that firefighters feared could exhibit "extreme fire behavior" during the windy, dry afternoon as it burned through oil-rich pine trees. That blaze, the Thompson Ridge fire, could threaten Native American archaeological sites in the Valles Caldera National Preserve, said Dana Howlett, a spokeswoman for the U.S. Forest Service. The Valles Caldera Preserve and its many archeological sites include six volcanic mounds important to the Pueblo of Zia indigenous group, according to the preserve's website. "With the intense heat, the fire gets more intense and you often have trees that are torching, and when that happens, large smoke plumes start going up," Howlett said. From a distance, she said, the dramatic flames and smoke can make it look like a volcano is erupting. The blaze threatened the small communities of Compton Valley, Rancho de la Cueva and Elk Valley, Howlett said. About 50 families, evacuated on Friday, remained out of their homes. Separately, the Tres Lagunas fire in New Mexico's Pecos Wilderness has burned nearly 8,000 acres with only 5 percent containment in the southern portion, said Fire Information Officer Dick Fleishman. The southern California blaze, dubbed the Powerhouse fire, grew by 10,000 acres during the day on Sunday and overnight into Monday, burning brush that turns to tinder in the dry California summer every year, U.S. Forest Service officer Ronald Ashdale said. The blaze, in the far northern portion of Los Angeles County, was 40 percent contained by Monday morning, he said, and a change in its direction meant fewer homes were now threatened: 400, down from 1,000. Despite cooler, wetter weather that moved into the region overnight, firefighters now believe it will take them until June 10 to contain the blaze, Ashdale said. For the first time in decades, the U.S. Forest Service is using night-flying helicopters to help fight the fire, a long-standing practice among other firefighters in the region, Ashdale said. In Colorado, a wildfire that erupted in the foothills west of Denver on Monday afternoon has prompted mandatory evacuations of homes within a four-mile radius around the blaze, fire officials said. The cause of the so-called Bluebell Fire was under investigation and there was no estimate on its size, said Jefferson County Sheriff's Office spokeswoman Jacki Kelley. Reporting by Sharon Bernstein in Los Angeles, Zeie Pollon in Santa Fe and Keith Coffman in Denver; Writing by Sharon Bernstein; Editing by Cynthia Johnston, Gary Hill and Steve Orlofsky