President Obama approved federal disaster aid late Thursday night for areas along Colorado's Front Range mountains after days of heavy rain caused flash flooding that left at least three dead and prompted authorities to evacuate thousands from cities like Boulder, Fox News reports. Gov. John Hickenlooper signed a disaster declaration and said, "This could easily be a 50- or 100-year flood." After a rainy week, up to 8 more 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 and into some cities, including Colorado Springs, Denver, Fort Collins, Greeley, Aurora and Boulder. 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. Late Thursday night, Boulder city officials said they sent a notice to head to higher ground to about 4,000 people living around the mouth of Boulder Canyon after 11 p.m. MDT. 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. An evacuation center for the mountain residents has been sent up in nearby Nederland, officials said. Meanwhile, about 400 students at the University of Colorado housing in Boulder were evacuated and classes canceled Friday because of the flooding. The school said it will assess the situation and determine when it will reopen portions of its campus. Emergency Management director Mike Chard said people should avoid creeks and waterways, and not attempt to cross flooded intersections in their cars.