LONGMONT, Colo. -- Coffee-colored floodwaters cascaded downstream from the Colorado Rockies on Friday, spilling normally scenic mountain rivers and creeks over their banks and forcing thousands more evacuations in water-logged communities beset by days of steady rain.
The relentless rush of water from higher ground turned whole towns into muddy swamps and threatened to strand hikers and some rural residents into the weekend. In at least one community, pressure from the descending water caused sewer grates to erupt into huge black geysers.
All the while, rain continued to fall, causing flooding across a wide rugged area stretching from Denver to Fort Collins.
The overflowing St. Vrain River cut the town of Longmont in half. Evacuation requests were issued for some neighborhoods, all major roads were closed and several thousand homes and businesses were without power.
National Guard troops were working to rescue more people stranded in Lyons and other communities in the foothills after conducting more than 100 evacuations Thursday, spokeswoman Cheresa Theiral said. Four helicopters were on search-and-rescue and reconnaissance operations in Boulder County and around Fort Collins.
About 90 miles of Interstate 25 were closed Friday from Denver to Cheyenne, Wyo., because of flooding from the St. Vrain, Poudre and Big Thompson rivers, transportation officials said.
So far, at least three people have been killed and another was missing. Hundreds more were forced to seek emergency shelter up and down Colorado's heavily populated Front Range, which has received more than 15 inches of rain this week, according to the National Weather Service.
That's about half the amount of precipitation that normally falls in the foothills near Boulder during an entire year.
Boulder County spokesman James Burrus said 20 people were unaccounted for Friday. But, he noted, that doesn't necessarily mean they are missing.
"It means we haven't heard back from them," Burrus said.
Two backpackers became stranded after the weather turned. Suzanne Turell and Connie Yang of York, Maine, last sent a text message Thursday with their GPS coordinates, but their cellphones have since gone dead, said Turell's mother, Barbara.
The National Park Service planned to mount a rescue effort for the hikers.
Late Thursday, warning sirens blared in Boulder, and city officials told about 4,000 people living along Boulder Creek to head for higher ground.
Debris and mud coming off the mountainsides had backed up water at the mouth of Boulder Canyon, causing the creek to rise rapidly, authorities said.
The creek began to recede after midnight, but the conditions remained dangerous, authorities said.
The water was a cafe-au-lait color, and debris indicated it had fallen more than two feet overnight.
The entire hamlet of Eldorado Springs, home to about 500 people, was also urged to evacuate because of a flash flood and mudslide threat along South Boulder Creek, Burrus said.
In Fort Collins, neighborhoods along the Cache La Poudre River were evacuated overnight, with the river expected to rise to nearly 2 feet above flood stage Friday, according to the weather service.
The city closed bridges after water began topping Seaman Reservoir in the Poudre Canyon. Residents were warned to stay clear of the river.
In Lyons, residents took shelter on higher ground, including some at an elementary school, before National Guard convoys could push through the water and into the isolated town. The convoys carried 15 people at a time to buses beyond the roadblocks, past cheering crowds.
To the south, the small community of Jamestown was also out of reach, along with 150 children stuck in summer camps nearby, Boulder County Sheriff's Cmdr. Heidi Prentup said.
The children have plenty of food and water, she said.
The weather service warned Friday of more flash flooding in Loveland. In the town of Drake, the Big Thompson River was more than 4 feet above flood stage. The Big Thompson caused the deadliest flash flood in state history in 1976, when about a foot of rain fell in just four hours, killing 144 people.
President Barack Obama signed an emergency declaration Thursday night, freeing federal aid and allowing the Federal Emergency Management Agency to coordinate disaster-relief efforts.
Some of the flooding was exacerbated by wildfire "burn scars" that have spawned flash floods all summer in the mountains. The flames strip away vegetation that normally helps absorbs excess water and leave a residue behind that sheds water.
One person was killed when a structure in Jamestown collapsed. Another man drowned in floodwaters north of Boulder, and a woman who was with him was missing. She was swept away after the vehicle she was riding in got stuck in water.
The man died after getting out of the vehicle to help her, police said.
To the south, Colorado Springs officers conducting flood patrols found the body of 54-year-old Danny Davis in Fountain Creek on the city's west side.
Associated Press writers Colleen Slevin, Steven K. Paulson and Thomas Peipert in Denver and Mead Gruver in Longmont contributed to this report.
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