LYONS, Colo. — Heavy rains sent walls of water crashing down mountainsides on Thursday in Colorado, killing at least three people, forcing the state’s largest university to close, and isolating remote towns across a rugged landscape that included areas blackened by recent wildfires.
After a rainy week, up to 8 more inches fell in an area from the Wyoming border south to the foothills west of Denver. Flooding extended along the Front Range mountains and into some cities, including Colorado Springs, Denver, Fort Collins, Greeley, Aurora, and Boulder.
Numerous roads and highways were washed out or made impassable by floods. Floodwaters poured into homes, and at least a few buildings collapsed in the torrent.
Boulder County appeared to be hardest hit. Sheriff Joe Pelle said the town of Lyons was completely cut off because of flooded roads.
Although everyone was believed to be safe, the deluge was expected to continue into Friday.
‘‘It is not an ordinary disaster,’’ Pelle said. ‘‘All the preparation in the world . . . it can’t put people up those canyons while these walls of water are coming down.’’
To the north, residents along the Big Thompson Canyon in Larimer County, scene of the deadliest flash flood in state history, were evacuated.
At the University of Colorado, about 400 students in a dorm were evacuated, and administrators canceled classes at least through Friday.