"In Boulder, the rainfall record for September set in 1940 was shattered..."

"... 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.

Boulder Creek, which runs through the heart of the city, became a raging torrent that burst its banks and flooded adjacent parking lots and streets as warning sirens wailed.