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Chris Schneider, Associated Press
A muddy U.S. flag stands in front of flooded homes in Longmont, Colo., on Saturday, Sept. 14, 2013. Floodwaters have affected a 4,500 square-mile section of the state. National Guard helicopters have been evacuating residents from the hardest hit communities.

LYONS, Colo. — Gerald Guntle dials his sister's home multiple times a day, desperate to find out if she survived the widespread flooding that shattered the Rocky Mountain foothill town of Lyons. But the phone just rings and rings.

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The Tucson, Ariz., man's sister is among hundreds of people listed as missing in a disaster that is already confirmed to have killed four people.

Officials hope the number of missing will drop rapidly as communications are restored and people are evacuated, as it did in Larimer and Boulder counties. Some 487 people in the two counties dropped off missing-persons list over the weekend.

Faced with a lack of information, friends and relatives are struggling to avoid thoughts of worst-case scenarios. Experts say the waiting can take a psychological toll.