From mountain towns east to the plains city of Fort Morgan, numerous Colorado communities remain cut off by flooding as rain continued to fall through the weekend and rescuers continued to make treacherous journeys up canyon roads to reach isolated homes.

Debris gathers in the corner of a fence in front of a home in La Salle, Colorado (Marc Piscotty/Getty Images)

The surging waters have been deadly, with four people confirmed dead and two more missing and presumed dead after their homes were swept away.

State emergency officials say some 1,500 homes have been destroyed and about 17,500 have been damaged. In addition, 11,700 people have fled their homes, and a total of more than 1,200 people have not been heard from.

As many as 1,000 people in Larimer County have been waiting for rescuers to reach them, but airlifts were grounded Sunday because of the rain.

Hundreds more people are unaccounted for to the south in Boulder County and other flood-affected areas. And the town of Lyons has been almost completely abandoned.

In Colorado, tropical air snagged on mountain range equals disaster

DENVER (AP) — Most residents of the Colorado Front Range don't pay much attention to the small streams that typically trickle past on their way from the mountains to the plains.

But that was before this past week, when more than a foot of rain from a storm system hung up on the Rocky Mountains supercharged those streams with a deadly force. The state now faces a long recovery from widespread devastation and four people confirmed dead.

Weather experts say the storm system was a rare event.

State climatologist Nolan Doesken says it started with an unusually moist air mass. That met a sprawling wind pattern that kept pushing the mass up against the Rocky Mountain foothills. The air rose, condensed, fell as rain and kept repeating.