Residents in northern Colorado continued to struggle today, as flash floods consumed whole neighborhoods and forecasts warned of more rain to come this weekend.

In Estes Park, trapped residents had to zip-line to safety, barely skimming the waters where lawns, streets and parks once stood. More than a year's worth of rain has fallen in less than three days. At least four people have been killed and 80 remain unaccounted for.

Colorado's extreme weather left two climbers stranded on Longs Peak

The six inches to a foot of water in Boulder left the city of 100,000 people cut off from rescue efforts. For some residents, escape was nearly impossible as water and mud surged into homes.

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"We got a call that there was a wall of water coming out, and so we went outside and climbed up above our house and we heard a big roar," said resident Jeff Writer, whose elderly neighbor was trapped in his bed by a landslide (the neighbor survived). "I think that's when it probably came down, buried his house [and] buried his bedroom full of mud."

Scenes from Colorado's dangerous floodwaters

For two hours, Roy Ortiz remained trapped in his Pontiac Grand Prix, after it was flung into the rapids Thursday by flash floods. The father of four said even as another car sent the Grand Prix deeper underwater, he tried to calm himself as rescuers worked to free him.

"I had to pray … because I want to survive," Ortiz said today as he left the hospital. "[Now] I'm feeling good. Thanks to God and my family and the rescue people who saved my life."

Communities remain cut off, rivers have gnawed away at roads and river and creek beds have spilled over as hundreds have been forced to evacuate. Interstate 25 was shut down for 70 miles, all the way to the Wyoming state line. Boulder Creek reportedly raged at 120 times its normal rate.

In Colorado's Boulder County, rescue operations had to be repeated over and over again. The waters were starting to recede today in Boulder, but officials warned that conditions were still dangerous.

"A foot and a half or two feet of water doesn't look like it's life threatening, but it is," said Gov. John Hickenlooper. "This water is filled with debris and sand and it is almost like liquid cement that can … knock people over and you can be swept away."

Evacuees from Lyons - stranded as the waters rose - were finally able to reach dry land after the National Guard arrived Thursday night. The National Guard has evacuated more than 300 so far.

ABC News' Ginger Zee, Brandi Hitt and Clayton Sandell contributed to this story.

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