A police officer allows a special dive rescue team to pass on a closed road following overnight flash flooding in downtown Boulder, Colo., on Thursday. LYONS, Colo. — Heavy rains sent walls of water crashing down mountainsides Thursday in Colorado, cutting off remote towns, forcing the state’s largest university to close and leaving at least three people dead across a rugged landscape that included areas blackened by recent wildfires.A warm, moist storm system has been dropping rain on the region for much of the week. Up to 8 inches fell in an area spanning from the Wyoming border south to the foothills west of Denver. Flooding extended all along the Front Range mountains, including the cities of Colorado Springs, Denver, Fort Collins, Greeley, Aurora and Boulder.Numerous roads have been washed out or made impassable by floods, and water has poured into homes. Some buildings have collapsed in the torrent. Parts of several interstate highways in the Denver area were temporarily closed because of standing water.Boulder County appeared to be hardest hit. Sheriff Joe Pelle said the town of Lyons was completely cut off because of flooded roads, and residents were huddling together on higher ground. Although everyone was believed to be safe, the deluge was expected to continue into Friday.Search vehicles and rescue helicopters were standing by, but many were unable to get to mountain communities because of flooding and fog. Residents were asked to drink bottled or boiled water because of possible contamination to water supplies.