The unusual late-summer downpours drenched Colorado's biggest urban centers, stretching 130 miles along the eastern slopes of the Rockies from Fort Collins near the Wyoming border south through Boulder, Denver and Colorado Springs. 

In Boulder, the rainfall record for September set in 1940 was shattered, officials said, unleashing surging floodwaters in Boulder Canyon above the city that triggered the evacuation of some 4,000 residents late on Thursday. 

"There's so much water coming out of the canyon, it has to go somewhere, and unfortunately it's coming into the city," said Ashlee Herring, spokeswoman for the Boulder office of Emergency Management.