Firefighters battled a massive wildfire threatening hundreds of homes and buildings as well as ancient Indian lands in New Mexico, officials said. The federal Incident Management Team said the Las Conchas fire, about 19 percent contained, burned more than 121 acres and destroyed more than 100 buildings, CNN reported. \"We are not out of the woods yet,\" said Brad Pitassi, spokesman for the Incident Management Team the Southwest. \"This will take a long time to contain.\" The federal incident team said the fire threatened 410 structures as of early Monday. It burned thousands of acres on the Santa Clara Indian Reservation and spread onto the Bandelier National Monument, where ancient Pueblo homes, rock paintings and petroglyphs can be found, fire officials said. Health and environmental officials warned that heavy smoke and ash were creating unhealthy air quality in Albuquerque, Santa Fe and Taos, warning that the elderly, children and people with heart or lung problems to stay indoors. Alamos County Police Chief Wayne Torpy said the majority of roadblocks around the county were removed and about 10,000 residents were allowed to return home during the weekend, CNN reported. Besides evacuations, the fire prompted the closure of Los Alamos National Laboratory, which will reopen to employees Wednesday. Investigators determined the fire, which started June 26, was sparked after an aspen tree knocked down by strong winds hit a power line and caught fire, New Mexico State Forester Tony Delfin said. The tree fell to the ground and sparked vegetation close by. Elsewhere, The Albuquerque Journal reported the Little Lewis Fire near Weed, N.M., was about 90 percent contained after burning about 1,100 acres as of Sunday morning.