(CNN) -- The steep, picturesque canyons that wind through Colorado's northern Front Range have been a draw for tourists, day-trippers and homebuyers for more than a century. But when record-setting rainfall began to hit last week, those picturesque canyons became funnels that poured hundreds of tons of water per second into towns like Boulder, Longmont and Lyons and left hundreds stranded in the mountains above. "This flood was a direct result of the large amount of rainfall that occurred in a widespread area, essentially from Denver north to almost the Wyoming state line, and for a long duration -- for about a 48-hour period last week," said Robert Kimbrough, a hydrologist with the U.S. Geological Survey in Denver.
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Boulder County says only 4 still unaccounted for
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Boulder saw nearly half its annual rainfall in a single day
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"It all happened fairly quickly," a scientist says
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Nebraska warily watches the rising South Platte
Now the runoff is coursing down the South Platte into neighboring @placeholder, where forecasters are warning of flooding into the weekend.