LONGMONT, Colo. (AP) — Construction crews and National Guard troops are working furiously to repair highways to mountain towns cut off by unprecedented Colorado flooding.

State officials drove and hiked along one heavily damaged highway on Sunday and said they're optimistic they can meet a Dec. 1 target to complete temporary fixes.

The flood obliterated sections of roadways as long as football fields.

Officials say it's too early to know how much time and money it will take to make permanent repairs, but they say it will cost more than $100 million.

The floods killed seven people. Three others are missing and presumed dead. Sixty people are unaccounted for, but that number is dropping as roads and phone service are restored.

Some 200 miles of state highways and 50 bridges were destroyed.

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