More than 200 firefighters worked through the night trying to contain the blaze, which began Tuesday when a yard fire got out of control about 70 miles northwest of Denver.
The fire was 15 percent contained by Friday, but officials were not relieved. An evacuation warning was issued for 140 homes in two subdivisions and the hamlet of Livermore, on the fire's northern edge, was placed on alert.
Fire crews, hampered by warm temperatures and low humidity, hoped an expected spring storm would help them get a handle on the inferno. Some moisture was expected by Friday morning, along with temperatures in the 50s.
Efforts were also hampered by gray smoke, which billowed thousands of feet into the sky and grounded air tankers at 5 p.m. Thursday.
``Smoke was so thick, they had to put them down,'' Lee said.
Earlier in the day, Sheriff Jim Alderden said he saw 100-foot flames as the fire raced through heavy timber.
Standing at the entrance of the Bonner Peak subdivision, Andy Martinez watched the smoke with his wife and two children. He had been awakened at 5 a.m. by a warning call from authorities and had gone outside to trim shrubs and other potential fuels.
The family left five hours later, bringing a few possessions and the dog. Left behind were a horse and two cats.
``As long as we had our kids, that's all that mattered,'' said Martinez, 38. ``It's kind of surreal. You wish it wasn't happening to you.''
As a smoky haze settled over nearby Fort Collins, shelters were set up at a church and junior high school for evacuees, who were asked to leave a towel on the door knob to show their home was empty.
Firefighting costs reached at least $220,000. The Federal Emergency Management Agency approved federal aid to help fight the fire.
At his four-bedroom brick and stucco home, Terry Guriel had his horses in a trailer and said he was ready to leave on 10 minutes' notice. The fire, he said, was still ``a ridge or so'' away.
``We've had grass fires here before, but nothing of this magnitude,'' he said.
The fire is an ominous sign of what could be a long, devastating fire season. Colorado, like much of the West, remains stuck in a drought with little sign of relief.
In central Arizona, a persistent rain helped firefighters contain a wildfire near the rural community of Pine at 4,311 acres.
Containment had originally been projected for Friday evening but Thursday's rains sped up the process. ``Mother nature helped us finish it off,'' said Myndi Brogdon, a fire spokeswoman.
The fire, which was originally reported Monday, briefly threatened a Boy Scout camp in the area but never damaged any structures.
A 5,700-acre fire southwest of Phoenix was contained Thursday.
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