Officials said that they evacuated Fourmile Canyon, to the west of Boulder, and Jamestown, to the north. They asked people to remain indoors and off the roads even as flood waters were expected to recede throughout the day.
"It may look OK in your neighborhood, but by the time you get on the thoroughfare to work, you may run into some real issues," Boulder County Sheriff Joe Pelle told local newspaper the Daily Camera. "We've got cars in water and debris and manholes missing their covers literally everywhere in the county."
The University of Colorado Boulder said on its Twitter account that its campus would be closed Thursday, until officials could assess the storm damage, and some residences were evacuated. Between 400 and 500 graduate students, faculty, and staff are thought to be displaced from on-campus housing units, said university spokesman Bronson Hilliard, and there may be "minor damage" to some buildings.
"We are pleading with students and people on this campus to stay indoors," Ryan Huff, a spokesman for the campus police, said at a press conference early Thursday morning. "It is dangerous out there."
An earth dam in the Big Elk Meadows area collapsed, according to the Larimer County Sheriff's office, causing officials to warn people in the path of the water to be ready to make their way to higher ground if necessary. The sheriff's office said on its Twitter feed that "extrication operations" were underway and that the amount of water thought to have escaped the dam was "relatively small."
The area is thinly populated, NBC News affiliate KUSA reported.
The sheriff's office requested a National Guard helicopter to rescue several families trapped after a road was washed away in Larimer County.
"The road is completely gone," a spokeswoman said. "They have no way of getting out."
Sheriffs in Boulder County were unable to reach the area of the fatality near Jamestown because of thick mud and rock slides.
Authorities have warned people to stay awake from creeks and other waterways as every available fire and police official was out on the streets, Boulder city spokeswoman Sarah Huntley said on Thursday. Flood sirens have been activated along Boulder Creek, and if there are sudden flash floods, "the warnings are going to be short," she said.
Shelters have been opened for evacuated or displaced residents at the YMCA in Boulder, an elementary schools in Jamestown and Lyons, as well as in Longmont and at the Nederland Community Center, according to Boulder's emergency management office.
—Christopher Nelson of NBC News and David Wyllie of BreakingNews.com contributed to this report. The Associated Press also contributed.