President Obama ordered federal aid to Colorado Saturday night after thousands of residents were driven from their homes when floodwaters cascaded downstream from the Rockies, stranding hikers and residents in rural communities slammed by days of steady rain.

Meanwhile, more storms caused flooding in southern and eastern portions of the Denver metro area Saturday afternoon, as officials reported that more than 500 people were unaccounted for.

The president signed a federal disaster declaration Saturday evening. The White House said in a statement that the action makes federal funding available to affected individuals in Boulder County, thought other counties could be added later. 

Rescuers issued stern warnings Saturday to anyone thinking of staying behind: Leave now or be prepared to endure weeks without electricity, running water and basic supplies. 

National Guard helicopters and truck convoys carried the admonition into paralyzed canyon communities where thousands of stranded residents were eager to escape the Rocky Mountain foothills. But not everybody was willing to go. Dozens of people in the isolated community of Jamestown wanted to stay to watch over their homes.

"Essentially, what they were threatening us with is, 'If you stay here, you may be here for a month,'" said 79-year-old Dean Hollenbaugh, who was evacuated by Chinook helicopter from Jamestown, northwest of Boulder.

Special education teacher Brian Shultz, 38, was torn about leaving his Jamestown home.

"I was thinking about staying. I could have lasted at least a year. I have a lot of training in wilderness survival," he said, adding that he probably had enough beer to last the whole time.

As he sat outside a makeshift shelter at a high school, Shultz floated the idea of walking back into the funky mountain town.

"If we hike back, I would stay there and just live. I'd rather be at our own house than staying at some other people's houses," he said.

His wife, Meagan Harrington, gave him a wry smile. About 10 of their neighbors declined to evacuate, she said.

"They said they wouldn't force you, but it was strongly encouraged," she said.

Shultz teared up behind his sunglasses as he compared his situation to that of his neighbors.

"At least all of our stuff's there and will be there when we get back. The people right by the river, their houses were washed away. Other people thought their houses were going to be OK, and then they started to go. It's just really devastating."

By Saturday night, 1,750 people and 300 pets had been evacuated from Boulder and Larimer County, National Guard Lt. James Goff said. The airlifts will continue Sunday with helicopter crews expanding their searches east to include Longmont, Fort Collins and Weld County.

It was not clear how many people were still stranded.

The Denver Post reported that authorities believed that a 60-year-old woman from Cedar Cove was the fifth person killed by the flooding. Officials expect to find more bodies as the waters recede. 

The flooding has affected parts of a 4,500-square-mile area, almost the size of Connecticut.

Boulder County Sheriff Joe Pelle told KDVR.com that although floodwaters have started to recede, officials do not yet know how many structures were lost.

"Please be patient. This is an unprecedented event," Pelle told residents.

For those awaiting an airlift, Guardsmen dropped food, water and other supplies in Jamestown and other small towns in the winding, narrow canyons that dot the Rocky Mountain foothills.

Thousands of evacuees sought shelter in cities that were nearly surrounded by raging rivers spilling over their banks.

One was Mary Hemme, 62, who displayed a pair of purple socks as she sat outside the Lifebridge Christian Church in Longmont. They're a memento of the more than 30 hours she spent in an elementary school in the flood-stricken mountain town of Lyons. Many evacuees — eventually rescued by National Guard trucks — got socks because most of them had wet feet, Hemme said.

She recalled the sirens blared at 2:30 a.m. Wednesday.

"Mary we have to go, this place is flooding," she recalled her friend Kristen Vincent saying as they clambered out of a trailer.

"And we stepped out of the trailer, onto the ground where the cars were parked, and it already like this, almost to our knees," she said. "It wasn't just sitting there. It was rushing at us."

Soon the trailer, like others in the park where she was staying, was submerged.

Hemme said she walked up at hill a daybreak and surveyed the trailer park.

"The most terrifying thing was when I climbed up on that cliff and looked down. It was the meanest, most — I mean, no wonder it carries cars like toys," Hemme said. "I was so afraid that I was going to die, that water came so fast."

The dayslong rush of water from higher ground has turned towns on Colorado's expansive eastern plains into muddy swamps. Crews used inflatable boats to rescue families and pets from stranded farmhouses. Some evacuees on horseback had to be escorted to safe ground.

Near Greeley, some 35 miles east of the foothills, broad swaths of farmland had become lakes, and hundreds of roads were closed or damaged by floodwaters. A 70-mile stretch of Interstate 25 was closed from Denver to the Wyoming line.

Rocky Mountain National Park closed Friday, its visitors forced to leave via the 60-mile Trail Ridge Road to the west side of the Rockies.

It will be weeks, if not months, before a semblance of normalcy returns to Lyons, a gateway community to the park. The town, surrounded by sandstone cliffs whose color was reflected in the raging St. Vrain River, consisted of six islands Friday as residents barbecued their food before it spoiled. Several people set up a tent camp on a hill.

Residents were being evacuated from Lyons, but Hilary Clark was left walking around her neighborhood Friday.

Two bridges that led into the area were washed away. Unlike other parts of Lyons that had been reached by the National Guard in high clearance trucks, no such help had arrived for Clark.

"We're surviving on what we got," she said. "Some of us have ponds in our backyard and we're using that water and boiling it."