Denver ? In a faint haze of gray smoke Tuesday, residents on the outskirts of Denver packed clothing, family photos and even a wedding dress in case they had to flee the largest wildfire in Colorado’s 126-year history.

Chris and Lori Sutton awoke at dawn to the smell of smoke drifting through an open bedroom window. Chris Sutton said the smoke in his hilly subdivision was so thick it was “like fog,” though it blew away a few hours later.

Chris Bossert, 11, packs up some belongings as he and his family prepare to evacuate their home in a subdivision in Roxborough Park southwest of Littleton, Colo. Hundreds of residents on the outskirts of Denver have been urged to leave their homes, and thousands more prepared for the possibility of evacuation.

“You’re not sure what to do. Do you stay? Go?” he asked, standing outside his home 23 miles southwest of Denver. His wife left for work in a car stuffed with a handful of their belongings. The fire was still 10 miles away but getting closer.

By evening, the wind-whipped blaze had grown to 87,000 acres and stretched for 15 miles along the Rockies foothills. It was moving slowly to the northeast, toward Denver, and was within 35 miles of outlying suburbs.

Hundreds of residents have left their homes, and Douglas County authorities urged the Suttons and more than 13,000 others near Sedalia 20 miles south of Denver to leave. Thousands more were told they may have to flee.

Fire information officer Joe Colwell said 400 people had been cleared out of their homes in Teller County. He also said crews were pulled off the fire’s southern lines as a safety measure.

The fire was one of at least eight burning across Colorado, including a 10,400-acre blaze that destroyed 28 homes near Glenwood Springs, about 150 miles west of Denver. That fire was only 5 percent contained, but thousands of people were allowed to return to their homes.

The blaze southwest of Denver was nowhere close to being contained, and officials said it was too dangerous to put firefighters on its northern fringes between the flames and homes in Douglas County, one of the fastest-growing in the country.

“There is such a tremendous amount of heat that you can’t put firefighters on the ground in front of it,” fire information officer Tony Diffenbaugh said.

Smoke forced the closure Tuesday of the Florissant Fossil Beds National Monument, Supt. Jean Rodeck said.

The fire was started Saturday by an illegal campfire. It exploded over the next day to become the largest fire ever in the state.