Numerous pockets of individuals in Colorado remained cut off by the flooding as Sunday's rain hampered the helicopter searches, and rescuers trekked by ground up dangerous canyon roads to reach some of those homes isolated since Wednesday.
The surging waters have been deadly, with four people confirmed dead and two more missing and presumed dead after their homes were swept away.
Some 1,500 homes have been destroyed and about 17,500 have been damaged, according to an initial estimate released by the Colorado Office of Emergency Management on its website.
In addition, 11,700 people left their homes, and a total of 1,253 people have not been heard from, state emergency officials said.
With phone service being restored to some of the areas over the weekend, officials hoped that number would drop as they contacted more stranded people.
As many as 1,000 people in Larimer County were awaiting rescue Sunday, but airlifts were grounded because of the rain, Type 2 Rocky Mountain Incident Management Team commander Shane Del Grosso said.
Hundreds more people are unaccounted for to the south in Boulder County and other flood-affected areas.