State officials estimated that 18,000 homes were destroyed or heavily damaged and 1,621 destroyed swept away by the rising waters. Emergency shelters and churches quickly filled with displaced families and pets. Some residents, like those in Lyons, were told it could be two to four weeks before they could return to their homes.

In Boulder, businesses were closed over the weekend, and officials at the University of Colorado reported that nearly 80 buildings on campus suffered some minor water damage in basements and lower levels. Graduate students in off-campus housing near Boulder Creek had to be evacuated, and 23 students in on-campus dorms were relocated, said Bronson Hilliard, CU Boulder spokesman. Classes were cancelled, and, at the end of last week, the campus was closed for two days to assess damage, he said.

Washed to Bedrock

At the peak of the storm on Friday, the Colorado Dept. of Transportation had closed more than 40 highways, including Interstate 25, north from Fort Collins to the Wyoming border, and I-70, west into the mountains, because of mudslides. Thirty major highways and 654 lane-miles of roads remained closed, some indefinitely, at midweek, due to heavy debris and large sections of missing pavement. Dozens of sinkholes were reported, and many city streets were blocked off or impassable due to high water, mud and storm debris. In some cases, the roads no longer exist.

One of the hardest-hit areas was the Big Thompson Canyon east of Estes Park, where the North Fork of the Big Thompson River surged 4.5 ft  above flood stage. At least 12 miles of Highway 34 through the canyon was washed away, according to the Larimer County Sheriff’s office.

“The road’s just not there. It was washed to the bedrock,” Larimer County Sheriff Justin Smith told the Denver Post on Friday. The high water trapped hundreds of people in the canyon, most of whom had to be rescued by helicopter.

The Big Thompson was also the site of a devastating 1976 flood, which occurred after a dam burst above Estes Park, killing 144 people and causing millions of dollars in damage. Water levels in the canyon during that flood rose to 9.31 ft, compared to 10.5 ft in this storm, county officials said.

Farther north, water in the Cache La Poudre River, through Poudre Canyon and west of Fort Collins, reached three feet above flood stage on Friday but washed away only a short section of roadway; no bridges were reported out. More than 6,000 homes and 700 businesses were damaged or destroyed in Larimer County alone.

CDOT engineers said that, as of Monday, 50 bridges across the region had been either destroyed or severely damaged, with hundreds more still to be inspected. The agency has dispensed five crews to inspect bridges and close them as needed. The biggest concerns, said CDOT bridge inspector Chad Jackson, are the bridge foundations and embankments, which may have been significantly eroded by the high, fast water. “The bridges themselves have fared pretty well,” he said. “The roads around them, not so much.”

The Transportation Dept.’s Federal Highway Administration has approved $5 million in “quick release” emergency aid for Colorado. In announcing the funding on Sept. 13, Transportation Secretary Anthony Foxx said, “These federal funds represent a down payment on our commitment to the people of Colorado.”