BOULDER, Colo. -- A Colorado wildfire that has destroyed 170 homes showed no signs of relenting Thursday as wind gusts of more than 40 mph fueled fears that the flames would move east from the Rocky Mountain foothills and into the heart of Boulder, where some residents were warned to be ready to flee.
Officials worried about a repeat of the devastation in the foothills, where neighborhoods once filled with million-dollar homes and scenic mountain cabins have become piles of smoking rubble. On one lot, all that survived was a tennis court. On others, all that's left are crumbling, ash-covered foundations.
Authorities told residents on the west side of Boulder to be prepared to evacuate if the wildfire moves into town. They urged people to remove lawn furniture, brush and propane tanks that could fuel the fire. The city also mowed grass in open spaces to reduce potential fuel and told residents to do the same.
The city encouraged residents to gas up and park their cars pointed toward the road for a speedy getaway, wet down yards and vegetation and pack up important documents, medication and other items in case they had to flee.
But the leader of the national team that took over management of the fire seemed to play down the threat. Jim Thomas told reporters late Thursday that he didn't see imminent danger for Boulder, although he added that conditions can change and there's always a risk of a major fire spreading.
"I'm not aware of any real threat to the city of Boulder right now," Thomas said.
A containment line has been dug around about 30 percent of the 10-square-mile fire, although the line isn't continuous. Thomas said he couldn't predict when the fire would be fully contained.
Boulder is a city of about 100,000 people that is home to the University of Colorado and the National Institute of Standards and Technology, a federal laboratory best known for running the atomic clock that's used to maintain the official U.S. time.
Authorities said the biggest fire danger was north of downtown and west of Broadway, one of Boulder's main thoroughfares. The federal lab is on Broadway farther south, and the edge of the campus is on the eastern side of the street. Many sorority and fraternity houses are on the western side.
By Thursday evening, west-northwest winds in the foothills had reached 15-25 mph with occasional gusts above 40 mph. The strongest winds were expected Friday morning, said National Weather Service meteorologist Scott Entrekin in Boulder. A red flag warning, signaling high fire danger, was in effect for the broader region through Friday evening.
It wasn't the first time that Boulder has faced a wildfire threat. The city has mountain parks and abundant public open space considered potential trouble spots when fires have started in the mountains. A January 2009 wildfire crept up to Boulder's northern outer edges, but the city escaped unscathed.
Sprinklers were running in yards in parts of west Boulder and people put bags into cars.
Joe Glynn hosed down his yard in northwest Boulder and his 9-year-old son, Daniel, sprayed water on city open space next to their lot. His family packed bags in case they had to flee, but Glynn -- who has witnessed two other wildfires -- said he would stay behind and protect his home of 19 years.
"I'm going to stand on the roof with a hose if necessary," he said.
In a neighborhood further south, Peter Cowan was gathering his credit cards, financial papers and pictures.
"I got the warning," Cowan said. "I'm not in a panic, but I'm not going to ignore it."
Caitlin Kolibas, 22, a University of Colorado senior who lives west of Broadway in an area called University Hill, said her parents in New Jersey were "trying to get me a little more concerned." The university held evening classes as usual.
"It sounds like more of an official precaution ... a superfluous precaution," said Spencer Everett, 22, of Phoenix, who just graduated from the school.
William Witte, who works at a bike store on the hill across from campus, took the warning to heart. He knows people who lost their home in the fire and is aware Boulder could be in trouble if the fire jumps over the last row of mountains.
"Everybody who lives here knows how bad the winds can be," Witte said.
The preparations in Boulder reflect the ferocity of the wildfire since it broke out Monday and spread over roughly 6,300 acres. It has since become one of the most destructive fires in Colorado, destroying more homes than any other blaze in state history.
About 3,500 people have been out of their homes for four days, and some have been frustrated with a lack of information about what was happening behind fire lines because they couldn't do more to help.
About 1,000 people were allowed to check on their homes Thursday morning. About 25 people refused to leave when the winds picked up and people were ordered out. Boulder County sheriff's Cmdr. Rick Brough said authorities know where the people are and will go door to door if the fire flares up again.
Other people have gotten around roadblocks by foot or bike.
Lee McCormack made a trip to his house early Thursday but was stopped at a roadblock in the afternoon. McCormack, who was riding a bicycle, had planned to get more belongings, including his car and his wife's favorite laundry detergent, but couldn't talk an officer into letting him through.
"It's shut down. It doesn't matter how much you plead," McCormack. "I gave the cop a Power Bar and he still wouldn't let me up there."
Authorities are investigating whether a vehicle crashing into a propane tank started the fire. A recording of a 911 call and other communications released by the sheriff's office chronicles reports of flames jumping to trees after the collision.
In steep canyons about five miles west of Boulder, firefighters tried to secure fire lines. But the powerful wind gusts in the forecast could spread the fire beyond the 20-mile-long perimeter.
Winslow Robertson, the operations chief for the fire, estimated firefighters have been able to contain 45 percent of the blaze. He said no more structures were lost Thursday.
The reported loss of homes surpasses that of the 2002 Hayman fire in southern Colorado, the most destructive in state history. It destroyed 133 homes and 466 outbuildings on 138,000 acres of more sparsely populated area.
Fire managers said as many 700 firefighters and support personnel and seven air tankers were assigned to fight the fire, considered the nation's top firefighting priority.
It's a busy end to a relatively quiet fire season. Nationwide, about 2.6 million acres have burned this summer, about 50 percent less than the 10 year average, said Ken Frederick, spokesman for the National Interagency Fire Center in Boise, Idaho.