Rain is normally soaked up by a sponge-like layer of pine needles and twigs on the forest floor. But wildfires incinerate that layer and leave a residue in the top layer of soil that sheds water. A relatively light rain can rush down charred hillsides into streambeds, picking up dirt, ash, rocks and tree limbs along the way. Narrow canyons aggravate the threat.
At the University of Colorado, about 400 students in a dorm were evacuated, and administrators canceled classes at least through Friday. About a quarter of the school's buildings have some kind of water damage.
One person was killed when a structure collapsed in the tiny town of Jamestown northwest of Boulder. Another person drowned in northern Boulder as he was trying to help a woman who was swept away in a torrent of water, authorities said. Boulder County sheriff's Cmdr. Heidi Prentup said the woman is still missing.
To the south, Colorado Springs police conducting flood patrols found the body of 54-year-old Danny Davis in Fountain Creek on the west side of the city.
Weather service meteorologist Bob Kleyla said a 20-foot wall of water was reported in Left Hand Canyon north of Boulder, and a firefighter radioed he was trapped in a tree. He said rescuers trying to get to him were initially blocked by debris.
"We did access him. They put him onto a sled and were able to take him across the creek, so he is getting treatment at this point," Prentup said.
The creek is usually "just a trickle," said nearby resident Carm Say. "You can walk across it and have fun. Now, as you can see, it's hitting houses."
At least one earthen dam gave way southeast of Estes Park, the gateway to Rocky Mountain National Park. Water levels could rise downstream as authorities release more water to ease pressure on dams. With debris piling up near bridges, downstream farming areas including Fort Lupton, Dacono and Plateville were also at risk.
In rural Morgan County, authorities urged ranchers to move cattle to higher ground as the mountain rains emptied onto the plains.
Rain showers and thunderstorms were expected through the night, with some storms capable of dumping an inch of water in 30 minutes, the weather service warned.
Associated Press writers Steven K. Paulson and Thomas Peipert in Denver contributed to this report.
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